Generally the beijing airport taxi system is chaotic as taxis can refuse you and are small in size.so if you have large luggage you will have to take a black taxi ( fare slightly more).
My experience is that most fares from the airport of any city in china to its downtown destination should not be more than Y120.
If the taxi does not drop you at the entrance of your hotel for whatever reason, a scam is about to happen and always insist on taxi receipts from the meter - useful in getting a refund when you report to the police