diff --git a/server-rs/crates/api-server/src/raw_image.rs b/server-rs/crates/api-server/src/raw_image.rs
index 2023ecec8..cea19316c 100644
--- a/server-rs/crates/api-server/src/raw_image.rs
+++ b/server-rs/crates/api-server/src/raw_image.rs
@@ -243,7 +243,7 @@ fn decode_image(value: RawImageData, field: &str) -> Result<ReferenceImage, AppE
     }
     reader
         .decode()
-        .map_err(|_| bad_request(format!("{field}.data 必须是有效 PNG 文件")))?;
+        .map_err(|error| map_decode_image_error(field, error))?;
     Ok(ReferenceImage {
         bytes,
         file_name: format!("{field}.png"),
@@ -251,6 +251,16 @@ fn decode_image(value: RawImageData, field: &str) -> Result<ReferenceImage, AppE
     })
 }
 
+fn map_decode_image_error(field: &str, error: image::ImageError) -> AppError {
+    let message = match error {
+        image::ImageError::Limits(_) => {
+            format!("{field}.data 超出 PNG 尺寸或解码资源上限（单边不超过 {RAW_IMAGE_MAX_EDGE}px）")
+        }
+        _ => format!("{field}.data 必须是有效 PNG 文件"),
+    };
+    bad_request(message)
+}
+
 async fn raw_image_edit_price(state: &AppState, width: u32, height: u32) -> Result<u32, AppError> {
     let tier = if width.max(height) > 1536 { "2K" } else { "1K" };
     state
@@ -373,4 +383,24 @@ mod tests {
             assert!(prepare_request(serde_json::from_value(payload).expect("request")).is_err());
         }
     }
+
+    #[test]
+    fn oversized_valid_png_reports_resource_limit() {
+        let payload = serde_json::json!({
+            "image": {
+                "data": encoded_png(RAW_IMAGE_MAX_EDGE + 1, 1),
+                "mimeType": "image/png"
+            },
+            "prompt": "edit",
+            "width": 1024,
+            "height": 1024
+        });
+        let parsed: RawImageEditRequest = serde_json::from_value(payload).expect("request");
+        let error = match prepare_request(parsed) {
+            Ok(_) => panic!("oversized PNG should fail"),
+            Err(error) => error,
+        };
+
+        assert!(format!("{error:?}").contains("超出 PNG 尺寸或解码资源上限"));
+    }
 }