forgot to mention.they got this cab in front of summer palace's gate. I feel there's always dirty business happen on the cab waiting outside tourist attraction.so better to walk yourself several hundreds meters more to get a cab driving on the street.

Exactly. At such spots I always walk around the next corner to get my cab there. Flagging down from the street is the safest bet in China. To avoid being given fake notes it just helps to get off the taxi, open the right door and then give the money to the driver. If he tries to switch the notes you will see it - if you sit in the back you won't. Much better is of course to always have enough 10/20/50 notes with you.

Can you could phone them? Maybe they would ask you to give the money to the poor or a charity from them.

If it was me, I would be so happy to hear that the cheater was caught by the police. I would just give the money to help someone, since it's too hard to get back to me.

And thank you for helping the police catch this man!