1. after 主要用于时间或次序，behind 主要用于位置：

He decided to leave after lunch. 他决定午饭后离开。

Summer comes after spring. 春去夏来。

The hospital is behind the post office. 医院在邮局后面。

【注】behind 有时也用于时间，表示迟于，主要用于behind time（迟，晚）这一习语：

The train was 20 minutes behind time. 火车晚点 20 分钟。

2. 两者都可用于引申义，after 侧重指追求、寻找、模仿等；而behind 则侧重指在背后、支持、落后等：

The police are after her. 警察在追捕她。

Many young people are after her. 许多年青人都追求她。

We are behind you completely. 我们完全支持你。

He is behind the others in maths. 他的数学不如别人。