diff --git a/src/models/Option.ts b/src/models/Option.ts
index 2ffa7ac..463aa9d 100644
--- a/src/models/Option.ts
+++ b/src/models/Option.ts
@@ -5,6 +5,11 @@ export const AI_PROVIDER_BASE_URLS = {
     deepseek: "https://api.deepseek.com/v1",
 } as const satisfies Record<"openai" | "deepseek", AbsoluteUrl>;
 
+export const AI_PROVIDER_DEFAULT_MODELS: Record<"openai" | "deepseek", string> = {
+    openai: "gpt-4o-mini",
+    deepseek: "deepseek-v4-flash",
+};
+
 export const OPTION_STORAGE_KEY = "brainrest_option";
 
 export type ThemePreference = "system" | "light" | "dark";
diff --git a/src/options/Onboarding.tsx b/src/options/Onboarding.tsx
index 6f629ce..81e75fa 100644
--- a/src/options/Onboarding.tsx
+++ b/src/options/Onboarding.tsx
@@ -6,6 +6,7 @@ import { PRODUCT_BOUNDARY_COPY } from "../ui/bridge";
 import { ensureAiOriginPermission } from "./ai-origin-permission";
 import {
     getProviderDefaultBaseUrl,
+    getProviderDefaultModel,
     joinProvider,
     PROVIDER_LABELS,
     type ProviderChoice,
@@ -105,6 +106,10 @@ export default function Onboarding({ onDone }: { onDone: () => void }) {
         if (defaultBaseUrl) {
             setBaseUrl(defaultBaseUrl);
         }
+        const defaultModel = getProviderDefaultModel(choice);
+        if (defaultModel) {
+            setModel(defaultModel);
+        }
     };
 
     const isLast = step === STEP_TITLES.length - 1;
diff --git a/src/options/SettingsPage.tsx b/src/options/SettingsPage.tsx
index de1156d..ae835eb 100644
--- a/src/options/SettingsPage.tsx
+++ b/src/options/SettingsPage.tsx
@@ -24,6 +24,7 @@ import { createLogger } from "../utils/logger";
 import { ensureAiOriginPermission } from "./ai-origin-permission";
 import {
     getProviderDefaultBaseUrl,
+    getProviderDefaultModel,
     joinProvider,
     PROVIDER_LABELS,
     type ProviderChoice,
@@ -162,6 +163,10 @@ export default function SettingsPage({ onOnboardingReset }: { onOnboardingReset:
         if (defaultBaseUrl) {
             setBaseUrl(defaultBaseUrl);
         }
+        const defaultModel = getProviderDefaultModel(choice);
+        if (defaultModel) {
+            setModel(defaultModel);
+        }
     };
 
     const changeThemePreference = async (preference: ThemePreference): Promise<void> => {
diff --git a/src/options/provider.ts b/src/options/provider.ts
index 7bd8987..99f1dda 100644
--- a/src/options/provider.ts
+++ b/src/options/provider.ts
@@ -1,4 +1,4 @@
-import { AI_PROVIDER_BASE_URLS, type Option } from "../models/Option";
+import { AI_PROVIDER_BASE_URLS, AI_PROVIDER_DEFAULT_MODELS, type Option } from "../models/Option";
 import type { AbsoluteUrl } from "../models/types";
 
 /** provider 下拉项：openai / deepseek / 自定义绝对 URL */
@@ -28,6 +28,10 @@ export function getProviderDefaultBaseUrl(choice: ProviderChoice): AbsoluteUrl |
     return choice === "custom" ? undefined : AI_PROVIDER_BASE_URLS[choice];
 }
 
+export function getProviderDefaultModel(choice: ProviderChoice): string | undefined {
+    return choice === "custom" ? undefined : AI_PROVIDER_DEFAULT_MODELS[choice];
+}
+
 export interface AiProviderConfig {
     provider: Option["aiProvider"];
     baseUrl: AbsoluteUrl;