Love this picture, great expression.
could i suggest a slightly tighter crop from the left?
I find the pink a little distracting, and the woman on the left would work well to balance out the composition.

Great image though!

hey Xiaoli,
i like this images a lot. infact i played around with it a little in lightroom and i have a few pointers.
like malc said, check the colour balance, feels a little bit too warm. but not too much!
I agree with accipiter, and you should have moved the composition down, but isnt hien sight a brilliant thing? I cropped the top of the wall down so that the man with his arms crossed was exactly on the line of the 1/3 rule.
there is also a slight purple tinge to the arch, i would try to desaturate it.
hope this helps, Rob