diff --git a/en/api/echarts-instance.md b/en/api/echarts-instance.md
index 670537e4..0b408944 100644
--- a/en/api/echarts-instance.md
+++ b/en/api/echarts-instance.md
@@ -737,7 +737,7 @@ Exports connected chart image; returns a base64 url; can be set to `src` of `Ima
 ```ts
 (opts: {
     // Specify which series the data will be appended to.
-    seriesIndex?: string,
+    seriesIndex?: number,
     // The data to be appended.
     data?: Array|TypedArray
 }) => string
diff --git a/zh/api/echarts-instance.md b/zh/api/echarts-instance.md
index 769886b1..91843261 100644
--- a/zh/api/echarts-instance.md
+++ b/zh/api/echarts-instance.md
@@ -724,7 +724,7 @@ img.src = myChart.getDataURL({
 ```ts
 (opts: {
     // 要增加数据的系列序号。
-    seriesIndex?: string,
+    seriesIndex?: number,
     // 增加的数据。
     data?: Array|TypedArray
 }) => string