Thank you all very much for the suggestions. I have somebody go there, the guests informed they would move out tomorrow morning. I hope they really do so.
Airbnb is good company, most of their staffs are very nice. While in some cases, hosts are so helpless when they DECIDED something. They could cancel guests' account before their checking in or after they checking out, it's very unreasonable to cancel their ACCOUNT during their stay, while refusing to provide me any info about the guests, due to "Privacy Policy". Come on, they are in our house due to our trust to you, and you just tell me that they are of high risky and you couldn't tell any more to us.
Will you think it's funny if one of your friends introduce somebody to live in your house at winter leave, and then said “they are of high risky and I couldn't tell you anything about them. Good luck."?
Another time, guests cancelled a reservation on their checking in date, and Airbnb just returned all their deposit and keep these days locked, until the Airbnb agent was back from her holiday, she remembered to unblock these days. No way to find her during her leave, and no way to complain to Airbnb customer service.
I hope Aibnb have more communications with hosts, so the company, hosts and guests would all feel happy.