diff --git a/app/api/canvas/generate/image/route.ts b/app/api/canvas/generate/image/route.ts
index d51b21610..e7f4725d2 100644
--- a/app/api/canvas/generate/image/route.ts
+++ b/app/api/canvas/generate/image/route.ts
@@ -25,7 +25,7 @@ function toGenerateImagePayload(body: GenerateImageRequest): CanvasGenerateImage
     aspectRatio:
       typeof body.aspectRatio === "string" && body.aspectRatio.trim()
         ? body.aspectRatio.trim()
-        : "1:1",
+        : "auto",
     imageSize:
       typeof body.imageSize === "string" && body.imageSize.trim()
         ? body.imageSize.trim()
diff --git a/app/canvas/[id]/page.tsx b/app/canvas/[id]/page.tsx
index 5ed5ba7b7..c32f5f19b 100644
--- a/app/canvas/[id]/page.tsx
+++ b/app/canvas/[id]/page.tsx
@@ -150,7 +150,7 @@ export default function CanvasEditorPage({ params }: PageProps) {
   // 生成配置
   const [prompt, setPrompt] = useState("");
   const [negativePrompt, setNegativePrompt] = useState("");
-  const [aspectRatio, setAspectRatio] = useState("1:1");
+  const [aspectRatio, setAspectRatio] = useState("auto");
   const [imageCount, setImageCount] = useState(1);
   const previousNodeIdsRef = useRef<Set<string>>(new Set());
   const selectedAgentPresetId = searchParams.get("agentPresetId");
@@ -505,9 +505,6 @@ export default function CanvasEditorPage({ params }: PageProps) {
 
     setGenerating(true);
     
-    // 获取尺寸预设
-    const sizePreset = SIZE_PRESETS.find(s => s.value === aspectRatio) || SIZE_PRESETS[0];
-    
     // 先创建占位节点（显示生成中状态）
     const placeholderNodeIds: string[] = [];
     for (let i = 0; i < imageCount; i++) {
diff --git a/lib/ai/providers/alibaba-image.ts b/lib/ai/providers/alibaba-image.ts
index f1e2552c9..8181b4558 100644
--- a/lib/ai/providers/alibaba-image.ts
+++ b/lib/ai/providers/alibaba-image.ts
@@ -503,12 +503,16 @@ export function createAlibabaImage({ apiKey, baseURL }: AlibabaImageConfig) {
               // 这里改为根据参考图比例计算 size，确保 1K/2K/4K 档位真正生效。
               const referenceImageUrl = imageUrls[imageUrls.length - 1];
               const inferredAspectRatio = await inferAspectRatioFromImageUrl(referenceImageUrl);
-              params.size = inferredAspectRatio
-                ? calculateAlibabaSizeByAspect(inferredAspectRatio, baseSize)
-                : `${baseSize}*${baseSize}`;
-              console.log(
-                `[Alibaba Image] Auto mode resolved size: imageSize=${imageSize}, inferredAspect=${inferredAspectRatio || "fallback-square"} => size=${params.size}`
-              );
+              if (inferredAspectRatio) {
+                params.size = calculateAlibabaSizeByAspect(inferredAspectRatio, baseSize);
+                console.log(
+                  `[Alibaba Image] Auto mode resolved size: imageSize=${imageSize}, inferredAspect=${inferredAspectRatio} => size=${params.size}`
+                );
+              } else {
+                console.log(
+                  `[Alibaba Image] Auto mode keeps provider default size: imageSize=${imageSize}, inferredAspect=unavailable`
+                );
+              }
             } else {
               const calculatedSize = calculateSize(aspectRatio, baseSize);
               if (calculatedSize) {
diff --git a/lib/canvas/generate-image.ts b/lib/canvas/generate-image.ts
index 33db7cfb5..c47da6947 100644
--- a/lib/canvas/generate-image.ts
+++ b/lib/canvas/generate-image.ts
@@ -85,7 +85,7 @@ export async function generateCanvasImage(
   const aspectRatio =
     typeof request.aspectRatio === "string" && request.aspectRatio.trim()
       ? request.aspectRatio.trim()
-      : "1:1";
+      : "auto";
   const imageSize =
     typeof request.imageSize === "string" && request.imageSize.trim()
       ? request.imageSize.trim()