图片的Texture Type设置为Cursor
Edit->Project Setting->Player->Default Cursor中设置，将更改好的图片拖拽赋值即可

    //要替换的光标图片
    public Texture2D cursorTexture;
 
    // Use this for initialization
    void Update () {
        Cursor.SetCursor(cursorTexture, Vector2.zero, CursorMode.Auto);
    }
 
    void OnMouseEnter () 
    {
        Cursor.SetCursor(cursorTexture, Vector2.zero, CursorMode.Auto);
    }
 
    void OnMouseExit () 
    {
        Cursor.SetCursor(null, Vector2.zero, CursorMode.Auto);
    }