我用Google搜索机器人模糊背景，发现这个博客帖子。基本上是：

I googled for "android blur background" and found this blog post. Basically:

dialog = new AlertDialog.Builder(this). /*... setTitle and so on ...*/ ;

WindowManager.LayoutParams lp = dialog.getWindow().getAttributes();  
lp.dimAmount=0.0f;  // this sets the amount of darkening
dialog.getWindow().setAttributes(lp);  
dialog.getWindow().addFlags(WindowManager.LayoutParams.FLAG_BLUR_BEHIND);

侨侨：）