easy是简单，pie是馅饼，easy as pie含义是易如反掌；小事一桩；极容易。

【例句】
The job was easy as pie, and we finished up an hour early.
这工作对我们来说是小事一桩，我们早在一小时前就完成了。

I finished the test paper in half an hour, because it's easy as pie.
我半个小时就考完试了，因为试题非常简单。