diff --git a/app/api/external/image/generate/route.ts b/app/api/external/image/generate/route.ts
index b37f18ef6..b6bf59261 100644
--- a/app/api/external/image/generate/route.ts
+++ b/app/api/external/image/generate/route.ts
@@ -12,6 +12,7 @@ import {
   ensureHostedReferenceImageUrls,
   generateImagesWithFailover,
   getRequesterIp,
+  normalizeExternalImageApiImageSize,
   resolveExternalImageApiOwnerUserId,
   serializeExternalImageApiModel,
   uploadExternalImageApiFile,
@@ -298,10 +299,11 @@ export async function POST(request: Request) {
   try {
     releaseExternalImageApiSlot = await acquireExternalImageApiSlot();
     const payload = await parseRequestPayload(request);
+    const imageSize = normalizeExternalImageApiImageSize(payload.imageSize);
     const candidateModels = await buildExternalImageApiModelCandidates({
       referenceImageCount: payload.referenceImages?.length || 0,
       aspectRatio: payload.aspectRatio,
-      imageSize: payload.imageSize,
+      imageSize,
     });
     const selectedModel = candidateModels[0];
     const ownerUserId = await resolveExternalImageApiOwnerUserId(
@@ -323,12 +325,13 @@ export async function POST(request: Request) {
         negativePrompt: payload.negativePrompt || null,
         imageCount: payload.imageCount || 1,
         aspectRatio: payload.aspectRatio || null,
-        imageSize: payload.imageSize || null,
+        imageSize,
         status: "pending",
         requesterIp,
         requesterUserAgent,
         requestPayload: {
           ...payload,
+          imageSize,
           candidateModels: candidateModels.map(serializeExternalImageApiModel),
           apiKeyFingerprint: buildExternalImageApiKeyFingerprint(
             authResult.accessKey,
@@ -345,7 +348,7 @@ export async function POST(request: Request) {
       negativePrompt: payload.negativePrompt || null,
       imageCount: payload.imageCount || 1,
       aspectRatio: payload.aspectRatio || null,
-      imageSize: payload.imageSize || null,
+      imageSize,
       referenceImageUrls: payload.referenceImages || [],
     });
     const actualModel = generationResult.usedModel;
@@ -367,7 +370,7 @@ export async function POST(request: Request) {
         optimizedPrompt: payload.prompt,
         requestedImageCount: payload.imageCount || images.length,
         aspectRatio: payload.aspectRatio,
-        imageSize: payload.imageSize,
+        imageSize,
         sourceImageUrls: payload.referenceImages || [],
         relationType: "edited_from",
         skipBilling: true,
diff --git a/lib/external-image-api/service.ts b/lib/external-image-api/service.ts
index 4d244ac60..8e8cdd62f 100644
--- a/lib/external-image-api/service.ts
+++ b/lib/external-image-api/service.ts
@@ -1,5 +1,6 @@
 import { createHash, timingSafeEqual } from "node:crypto";
 import { sql } from "drizzle-orm";
+import sharp from "sharp";
 import { getLanguageModelById } from "@/lib/ai/dynamic-provider";
 import { isImageGenerationModelDescriptor } from "@/lib/ai/model-classification";
 import { db } from "@/lib/db";
@@ -64,12 +65,25 @@ type ExternalImageApiGeneratedImage = {
   imageSize: string;
 };
 
+type ImageDimensionProbe = {
+  width: number;
+  height: number;
+  bytes: number;
+  contentType: string;
+};
+
+export const DEFAULT_EXTERNAL_IMAGE_API_IMAGE_SIZE = "1K";
+
 const logger = createLogger("external-image-api");
 
 function normalizeText(value: unknown) {
   return String(value || "").trim();
 }
 
+export function normalizeExternalImageApiImageSize(value?: string | null) {
+  return normalizeText(value) || DEFAULT_EXTERNAL_IMAGE_API_IMAGE_SIZE;
+}
+
 function mimeTypeToExtension(mimeType: string) {
   const normalized = mimeType.toLowerCase();
   if (normalized.includes("png")) return "png";
@@ -195,6 +209,92 @@ async function ensureHostedImageUrl(imageUrl: string): Promise<string> {
   return uploadRemoteImageToStorage(normalizedUrl);
 }
 
+async function probeRemoteImageDimensions(
+  imageUrl: string,
+): Promise<ImageDimensionProbe> {
+  const normalizedUrl = normalizeText(imageUrl);
+  if (!normalizedUrl) {
+    throw new Error("图片地址为空");
+  }
+
+  const response = await fetch(normalizedUrl, {
+    method: "GET",
+    cache: "no-store",
+    signal: AbortSignal.timeout(30_000),
+  });
+
+  if (!response.ok) {
+    throw new Error(`图片地址不可访问: HTTP ${response.status}`);
+  }
+
+  const contentType = response.headers.get("content-type")?.toLowerCase() || "";
+  if (contentType && !contentType.startsWith("image/")) {
+    throw new Error(`图片地址返回了非图片内容: ${contentType}`);
+  }
+
+  const buffer = Buffer.from(await response.arrayBuffer());
+  if (!buffer.length) {
+    throw new Error("图片内容为空");
+  }
+
+  const metadata = await sharp(buffer).metadata();
+  if (!metadata.width || !metadata.height) {
+    throw new Error("无法识别图片尺寸");
+  }
+
+  return {
+    width: metadata.width,
+    height: metadata.height,
+    bytes: buffer.byteLength,
+    contentType,
+  };
+}
+
+function getMinimumGeneratedOriginalLongestEdge(imageSize?: string | null) {
+  const normalized = normalizeText(imageSize).toUpperCase();
+  const exactSize = normalized.match(/(\d{3,5})\s*[X×]\s*(\d{3,5})/);
+  if (exactSize) {
+    const width = Number(exactSize[1]);
+    const height = Number(exactSize[2]);
+    if (Number.isFinite(width) && Number.isFinite(height)) {
+      return Math.max(768, Math.round(Math.max(width, height) * 0.65));
+    }
+  }
+
+  if (normalized.includes("4K")) return 1800;
+  if (normalized.includes("2K")) return 1000;
+  if (normalized.includes("1K")) return 768;
+  return 768;
+}
+
+async function assertGeneratedOriginalImagesAreLargeEnough(
+  images: ExternalImageApiGeneratedImage[],
+  imageSize?: string | null,
+) {
+  const minimumLongestEdge = getMinimumGeneratedOriginalLongestEdge(imageSize);
+  const requestedLabel = normalizeExternalImageApiImageSize(imageSize);
+  const probeCache = new Map<string, Promise<ImageDimensionProbe>>();
+
+  for (const image of images) {
+    const originalUrl = normalizeText(image.originalUrl || image.url);
+    if (!originalUrl) {
+      throw new Error("模型返回结果缺少原图地址");
+    }
+
+    if (!probeCache.has(originalUrl)) {
+      probeCache.set(originalUrl, probeRemoteImageDimensions(originalUrl));
+    }
+
+    const dimensions = await probeCache.get(originalUrl)!;
+    const longestEdge = Math.max(dimensions.width, dimensions.height);
+    if (longestEdge < minimumLongestEdge) {
+      throw new Error(
+        `模型返回原图尺寸过小: ${dimensions.width}x${dimensions.height}，未达到 ${requestedLabel} 输出要求`,
+      );
+    }
+  }
+}
+
 function toRecord(value: unknown): Record<string, unknown> | null {
   if (!value || typeof value !== "object" || Array.isArray(value)) return null;
   return value as Record<string, unknown>;
@@ -497,7 +597,7 @@ function parseGeneratedImageMarkdownMeta(alt: string, fallbackUrl = "") {
   const fallbackOriginalUrl = inferOriginalImageUrl(normalizeText(fallbackUrl));
   const originalUrl =
     extractOriginalImageUrlFromAlt(normalizedAlt, fallbackUrl) || fallbackOriginalUrl;
-  let imageSize = "2K";
+  let imageSize = DEFAULT_EXTERNAL_IMAGE_API_IMAGE_SIZE;
 
   if (normalizedAlt.includes("thumb|||")) {
     const parts = normalizedAlt
@@ -519,7 +619,7 @@ function parseGeneratedImageMarkdownMeta(alt: string, fallbackUrl = "") {
 
 export async function ensureHostedImageMarkdown(
   markdown: string,
-  imageSize = "2K",
+  imageSize = DEFAULT_EXTERNAL_IMAGE_API_IMAGE_SIZE,
 ) {
   const pattern = /!\[([^\]]*)\]\(([^)]+)\)/gim;
   const matches = [...markdown.matchAll(pattern)];
@@ -576,7 +676,7 @@ export function extractGeneratedImagesFromMarkdown(markdown: string) {
     const metadata = parseGeneratedImageMarkdownMeta(alt, thumbnailUrl);
     const originalUrl =
       metadata.originalUrl || inferOriginalImageUrl(thumbnailUrl) || thumbnailUrl;
-    const imageSize = metadata.imageSize || "2K";
+    const imageSize = metadata.imageSize || DEFAULT_EXTERNAL_IMAGE_API_IMAGE_SIZE;
     return {
       id: index + 1,
       url: originalUrl,
@@ -920,7 +1020,7 @@ export async function generateImagesWithFailover(params: {
 
       const hostedMarkdown = await ensureHostedImageMarkdown(
         markdown,
-        params.imageSize || "2K",
+        normalizeExternalImageApiImageSize(params.imageSize),
       );
       const images = extractGeneratedImagesFromMarkdown(hostedMarkdown);
 
@@ -928,6 +1028,11 @@ export async function generateImagesWithFailover(params: {
         throw new Error("模型返回结果里未解析到图片");
       }
 
+      await assertGeneratedOriginalImagesAreLargeEnough(
+        images,
+        normalizeExternalImageApiImageSize(params.imageSize),
+      );
+
       attempts.push({
         modelId: candidate.model.id,
         modelRuntimeId: candidate.model.modelId,