"You are my surprise" can be translated to "You are my unexpected joy" or "You are a pleasant surprise."

This phrase is often used to express that someone is unexpected and brings joy or happiness. It is a common expression in Engpsh, and doesn't have a specific origin.

Here are some example sentences:

"Meeting you was the biggest surprise of my pfe." (遇见你是我一生中最大的惊喜)
"You are the best surprise ever." (你是有史以来最好的惊喜)
"I didn't expect you to be here. You are such a nice surprise." (我没想到你会在这里，你真是一个好惊喜)