两个都可以用：

at the cinema 在电影院看电影 He is at the cinema, he is enjoying a movie.

in the cinema 在电影院里上班 He works in the cinema，he is at work now.

相关介绍

cinema：复数： cinemas

n.电影院;(去电影院)看电影;电影艺术;电影制片业

例句：

I prefer going to the cinema to watching TV.

我更喜欢看电影而不是看电视。

I myself enjoy cinema, poetry, eating out and long walks

我本人喜欢电影、诗歌、外出吃饭和远途散步。

Working with Ford closely, I fell in love with the cinema.

与福特的密切合作开始令我爱上了电影。

They decided to spend an evening at the cinema.

他们决定晚上去看电影。