diff --git a/src/App.tsx b/src/App.tsx
index 242c3a6..ef376b6 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -1,5 +1,4 @@
 import { useQuery } from "@tanstack/react-query";
-import { DateTime } from "luxon";
 import type React from "react";
 import { lazy, Suspense, useEffect, useState } from "react";
 import { useTranslation } from "react-i18next";
@@ -40,46 +39,57 @@ const MainApp: React.FC = () => {
 		retry: false,
 	});
 	const { i18n } = useTranslation();
-	const { setTheme } = useTheme();
+	const { setTheme, effectiveTheme } = useTheme();
 	const [isCustomCodeInjected, setIsCustomCodeInjected] = useState(false);
-	const { backgroundImage: customBackgroundImage } = useBackground();
+	const { backgroundImage: customBackgroundImage, updateBackground } =
+		useBackground();
 
 	useEffect(() => {
 		loadServerDetail();
 	}, []);
 
 	useEffect(() => {
-		const updateConfig = () => {
-			const config = settingData?.data?.config;
-			if (config) {
-				if (config.custom_code) {
-					InjectContext(config.custom_code);
-					setIsCustomCodeInjected(true);
-				}
-
-				// 同步自定义配置到全局变量
-				if (config.custom_logo) window.CustomLogo = config.custom_logo;
-				if (config.custom_description)
-					window.CustomDesc = config.custom_description;
-				if (config.custom_links) window.CustomLinks = config.custom_links;
-
-				const hour = DateTime.now().hour;
-				const isNight = hour >= 18 || hour < 6;
-
-				if (isNight && config.background_image_night) {
-					window.CustomBackgroundImage = config.background_image_night;
-				} else if (!isNight && config.background_image_day) {
-					window.CustomBackgroundImage = config.background_image_day;
-				}
-				window.CustomMobileBackgroundImage = window.CustomBackgroundImage;
+		const config = settingData?.data?.config;
+		if (config) {
+			if (config.custom_code) {
+				InjectContext(config.custom_code);
+				setIsCustomCodeInjected(true);
 			}
-		};
 
-		updateConfig();
-		const interval = setInterval(updateConfig, 60000); // Check every minute
-		return () => clearInterval(interval);
+			// 同步自定义配置到全局变量
+			if (config.custom_logo) window.CustomLogo = config.custom_logo;
+			if (config.custom_description)
+				window.CustomDesc = config.custom_description;
+			if (config.custom_links) window.CustomLinks = config.custom_links;
+
+			if (config.background_image_day) {
+				window.CustomBackgroundImageDay = config.background_image_day;
+			}
+			if (config.background_image_night) {
+				window.CustomBackgroundImageNight = config.background_image_night;
+			}
+		}
 	}, [settingData]);
 
+	// 监听有效主题以及配置变化，动态切换日夜背景
+	useEffect(() => {
+		const config = settingData?.data?.config;
+		const bgDay =
+			config?.background_image_day || window.CustomBackgroundImageDay;
+		const bgNight =
+			config?.background_image_night || window.CustomBackgroundImageNight;
+
+		const targetBg =
+			effectiveTheme === "dark"
+				? bgNight || window.CustomBackgroundImage
+				: bgDay || window.CustomBackgroundImage;
+
+		if (targetBg) {
+			updateBackground?.(targetBg);
+			window.CustomMobileBackgroundImage = targetBg;
+		}
+	}, [effectiveTheme, settingData, updateBackground]);
+
 	// 检测是否强制指定了主题颜色
 	const forceTheme =
 		(window.ForceTheme as string) !== "" ? window.ForceTheme : undefined;
diff --git a/src/components/ThemeProvider.tsx b/src/components/ThemeProvider.tsx
index 71143fc..e54dea7 100644
--- a/src/components/ThemeProvider.tsx
+++ b/src/components/ThemeProvider.tsx
@@ -19,11 +19,13 @@ type ThemeProviderProps = {
 type ThemeProviderState = {
 	theme: Theme;
 	setTheme: (theme: Theme) => void;
+	effectiveTheme: "light" | "dark";
 };
 
 const initialState: ThemeProviderState = {
 	theme: "system",
 	setTheme: () => null,
+	effectiveTheme: "light",
 };
 
 const ThemeProviderContext = createContext<ThemeProviderState>(initialState);
@@ -58,6 +60,17 @@ export function ThemeProvider({
 		};
 	}, []);
 
+	const effectiveTheme: "light" | "dark" = useMemo(() => {
+		if (theme === "system") {
+			return isSystemDark ? "dark" : "light";
+		}
+		if (theme === "scheduled") {
+			const isNight = hour >= 18 || hour < 6;
+			return isNight ? "dark" : "light";
+		}
+		return theme;
+	}, [theme, isSystemDark, hour]);
+
 	useEffect(() => {
 		const root = window.document.documentElement;
 
@@ -79,17 +92,6 @@ export function ThemeProvider({
 		};
 
 		root.classList.add("disable-transitions");
-
-		let effectiveTheme: "light" | "dark" = "light";
-		if (theme === "system") {
-			effectiveTheme = isSystemDark ? "dark" : "light";
-		} else if (theme === "scheduled") {
-			const isNight = hour >= 18 || hour < 6;
-			effectiveTheme = isNight ? "dark" : "light";
-		} else {
-			effectiveTheme = theme;
-		}
-
 		applyTheme(effectiveTheme);
 
 		const timeoutId = window.setTimeout(() => {
@@ -99,7 +101,7 @@ export function ThemeProvider({
 		return () => {
 			window.clearTimeout(timeoutId);
 		};
-	}, [theme, hour, isSystemDark]);
+	}, [effectiveTheme]);
 
 	const handleSetTheme = useCallback(
 		(nextTheme: Theme) => {
@@ -113,8 +115,9 @@ export function ThemeProvider({
 		() => ({
 			theme,
 			setTheme: handleSetTheme,
+			effectiveTheme,
 		}),
-		[theme, handleSetTheme],
+		[theme, handleSetTheme, effectiveTheme],
 	);
 
 	return (
diff --git a/src/hooks/use-background.ts b/src/hooks/use-background.ts
index 56d61fe..f88fe6d 100644
--- a/src/hooks/use-background.ts
+++ b/src/hooks/use-background.ts
@@ -1,8 +1,10 @@
-import { useEffect, useState } from "react";
+import { useCallback, useEffect, useState } from "react";
 
 declare global {
 	interface Window {
 		CustomBackgroundImage: string;
+		CustomBackgroundImageDay?: string;
+		CustomBackgroundImageNight?: string;
 		CustomMobileBackgroundImage: string;
 		ForceShowServices: boolean;
 		ForceCardInline: boolean;
@@ -17,7 +19,7 @@ const BACKGROUND_CHANGE_EVENT = "backgroundChange";
 
 export function useBackground() {
 	const [backgroundImage, setBackgroundImage] = useState<string | undefined>(
-		undefined,
+		() => window.CustomBackgroundImage || undefined,
 	);
 
 	useEffect(() => {
@@ -61,10 +63,10 @@ export function useBackground() {
 		};
 	}, []);
 
-	const updateBackground = (newBackground: string | undefined) => {
+	const updateBackground = useCallback((newBackground: string | undefined) => {
 		window.CustomBackgroundImage = newBackground || "";
 		window.dispatchEvent(new Event(BACKGROUND_CHANGE_EVENT));
-	};
+	}, []);
 
 	return { backgroundImage, updateBackground };
 }
diff --git a/src/lib/custom-config.ts b/src/lib/custom-config.ts
index 19eda64..1e60757 100644
--- a/src/lib/custom-config.ts
+++ b/src/lib/custom-config.ts
@@ -2,15 +2,38 @@ import { DateTime } from "luxon";
 
 export function initCustomConfig() {
 	try {
+		// Default day / night background images
+		window.CustomBackgroundImageDay =
+			window.CustomBackgroundImageDay ||
+			"https://loohui.com/wp-content/uploads/images/background_day.jpg";
+		window.CustomBackgroundImageNight =
+			window.CustomBackgroundImageNight ||
+			"https://loohui.com/wp-content/uploads/images/background.jpg";
+
+		const savedTheme = localStorage.getItem("vite-ui-theme");
+		const systemDark =
+			typeof window !== "undefined" && window.matchMedia
+				? window.matchMedia("(prefers-color-scheme: dark)").matches
+				: false;
 		const hour = DateTime.now().hour;
-		const isNight = hour >= 18 || hour < 6;
+		const isScheduledNight = hour >= 18 || hour < 6;
 
-		// Use default values if window variables are not already set (e.g. by backend custom_code)
-		// although the goal is to hardcode these for "consistency".
+		let isDark = false;
+		if (savedTheme === "dark") {
+			isDark = true;
+		} else if (savedTheme === "light") {
+			isDark = false;
+		} else if (savedTheme === "scheduled") {
+			isDark = isScheduledNight;
+		} else if (savedTheme === "system") {
+			isDark = systemDark;
+		} else {
+			isDark = isScheduledNight;
+		}
 
-		window.CustomBackgroundImage = isNight
-			? "https://loohui.com/wp-content/uploads/images/background.jpg"
-			: "https://loohui.com/wp-content/uploads/images/background_day.jpg";
+		window.CustomBackgroundImage = isDark
+			? window.CustomBackgroundImageNight
+			: window.CustomBackgroundImageDay;
 
 		window.CustomMobileBackgroundImage = window.CustomBackgroundImage;
 
diff --git a/src/test/app.test.tsx b/src/test/app.test.tsx
index 87cd41e..10a1475 100644
--- a/src/test/app.test.tsx
+++ b/src/test/app.test.tsx
@@ -9,6 +9,8 @@ const appMocks = vi.hoisted(() => ({
 	fetchSetting: vi.fn(),
 	injectContext: vi.fn(),
 	setTheme: vi.fn(),
+	updateBackground: vi.fn(),
+	effectiveTheme: "light" as "light" | "dark",
 }));
 
 vi.mock("../components/DashCommand", () => ({
@@ -38,11 +40,17 @@ vi.mock("../pages/ServerDetail", () => ({
 }));
 
 vi.mock("../hooks/use-background", () => ({
-	useBackground: () => ({ backgroundImage: appMocks.backgroundImage }),
+	useBackground: () => ({
+		backgroundImage: appMocks.backgroundImage,
+		updateBackground: appMocks.updateBackground,
+	}),
 }));
 
 vi.mock("../hooks/use-theme", () => ({
-	useTheme: () => ({ setTheme: appMocks.setTheme }),
+	useTheme: () => ({
+		setTheme: appMocks.setTheme,
+		effectiveTheme: appMocks.effectiveTheme,
+	}),
 }));
 
 vi.mock("../lib/inject", () => ({
@@ -90,7 +98,11 @@ describe("App", () => {
 		appMocks.fetchSetting.mockResolvedValue(settingResponse());
 		appMocks.injectContext.mockResolvedValue(undefined);
 		appMocks.setTheme.mockClear();
+		appMocks.updateBackground.mockClear();
+		appMocks.effectiveTheme = "light";
 		window.ForceTheme = "";
+		window.CustomBackgroundImageDay = "/day.png";
+		window.CustomBackgroundImageNight = "/night.png";
 		localStorage.clear();
 	});
 
@@ -202,4 +214,55 @@ describe("App", () => {
 		expect(await screen.findByText("server-page")).toBeInTheDocument();
 		expect(appMocks.setTheme).not.toHaveBeenCalledWith("dark");
 	});
+
+	it("updates background to day background when effective theme is light", async () => {
+		appMocks.effectiveTheme = "light";
+		window.CustomBackgroundImageDay = "/day.png";
+		window.CustomBackgroundImageNight = "/night.png";
+
+		renderApp();
+
+		await waitFor(() => {
+			expect(appMocks.updateBackground).toHaveBeenCalledWith("/day.png");
+		});
+		expect(window.CustomMobileBackgroundImage).toBe("/day.png");
+	});
+
+	it("updates background to night background when effective theme is dark", async () => {
+		appMocks.effectiveTheme = "dark";
+		window.CustomBackgroundImageDay = "/day.png";
+		window.CustomBackgroundImageNight = "/night.png";
+
+		renderApp();
+
+		await waitFor(() => {
+			expect(appMocks.updateBackground).toHaveBeenCalledWith("/night.png");
+		});
+		expect(window.CustomMobileBackgroundImage).toBe("/night.png");
+	});
+
+	it("applies day and night background images from backend settings config", async () => {
+		appMocks.effectiveTheme = "light";
+		appMocks.fetchSetting.mockResolvedValue({
+			success: true,
+			data: {
+				config: {
+					...settingResponse().data.config,
+					background_image_day: "/backend-day.png",
+					background_image_night: "/backend-night.png",
+				},
+				version: "1.0.0",
+			},
+		});
+
+		renderApp();
+
+		await waitFor(() => {
+			expect(appMocks.updateBackground).toHaveBeenCalledWith(
+				"/backend-day.png",
+			);
+		});
+		expect(window.CustomBackgroundImageDay).toBe("/backend-day.png");
+		expect(window.CustomBackgroundImageNight).toBe("/backend-night.png");
+	});
 });
diff --git a/src/test/components/ThemeProvider.test.tsx b/src/test/components/ThemeProvider.test.tsx
index 3fbb659..526c711 100644
--- a/src/test/components/ThemeProvider.test.tsx
+++ b/src/test/components/ThemeProvider.test.tsx
@@ -9,11 +9,12 @@ import {
 import { useTheme } from "@/hooks/use-theme";
 
 function ThemeProbe() {
-	const { setTheme, theme } = useTheme();
+	const { setTheme, theme, effectiveTheme } = useTheme();
 
 	return (
 		<div>
 			<p data-testid="theme-state">{theme}</p>
+			<p data-testid="effective-theme-state">{effectiveTheme}</p>
 			<button type="button" onClick={() => setTheme("dark")}>
 				dark
 			</button>
@@ -43,11 +44,17 @@ describe("ThemeProvider", () => {
 		);
 
 		expect(screen.getByTestId("theme-state")).toHaveTextContent("system");
+		expect(screen.getByTestId("effective-theme-state")).toHaveTextContent(
+			"light",
+		);
 		expect(document.documentElement).toHaveClass("light");
 
 		await user.click(screen.getByRole("button", { name: "dark" }));
 
 		expect(screen.getByTestId("theme-state")).toHaveTextContent("dark");
+		expect(screen.getByTestId("effective-theme-state")).toHaveTextContent(
+			"dark",
+		);
 		expect(localStorage.getItem("theme-test")).toBe("dark");
 		expect(document.documentElement).toHaveClass("dark");
 		expect(document.documentElement.style.colorScheme).toBe("dark");
@@ -57,6 +64,10 @@ describe("ThemeProvider", () => {
 		);
 
 		await user.click(screen.getByRole("button", { name: "light" }));
+		expect(screen.getByTestId("theme-state")).toHaveTextContent("light");
+		expect(screen.getByTestId("effective-theme-state")).toHaveTextContent(
+			"light",
+		);
 		expect(document.documentElement).toHaveClass("light");
 	});
 
diff --git a/src/vite-env.d.ts b/src/vite-env.d.ts
index 672cd18..473c14d 100644
--- a/src/vite-env.d.ts
+++ b/src/vite-env.d.ts
@@ -2,6 +2,8 @@
 
 interface Window {
 	CustomBackgroundImage: string;
+	CustomBackgroundImageDay?: string;
+	CustomBackgroundImageNight?: string;
 	CustomMobileBackgroundImage: string;
 	ForceTheme: string;
 	CustomLogo: string;