<?xml version="1.0" encoding="UTF-8"?>
<inset xmlns:android="http://schemas.android.com/apk/res/android"
    android:insetLeft="50dp"
    android:insetRight="50dp" >
    <shape>
        <solid android:color="@color/orange" />
        <corners android:radius="2.0dip" />
    </shape>
</inset>

参考：

How to assign padding to Listview item divider line