区别就是两者意思是不一样，具体的不同如下

in my face中文意思是当着我的面

I told my sister about my opinions, but she just laughed in my face.我告诉我姐姐我的想法，她却当面把我嘲笑了一番。

I felt a current of cool air blowing in my face.

on my face中文意思是在我脸上

When the glasses arrived, the eye doctor put them on my face and walked me out onto the sidewalk in front of his office.

in my face释义为

[网络] 都显示在我的脸上；咄咄逼人；在我脸上

my face: 我的脸

get out of my face: 从我面前消失; 离开我的视线、滚开; ...

his face on my pillow: 就像他的脸在我的枕头旁; 就象他的脸 ...

on my face释义：

在我的脸上

例句：

A rush of air on my face woke me.

脸上的一股急促的气流惊醒了我。