If we will only be in china for 72 hours do we need to do anything in advance?

Hi, may I know which city you will transit through? if it is Beijing, Shanghai, Guangzhou or Chengdu, you should inform United Airline about your need of transit for 72 hours so that the airline will mail your information to the airport then the free transit permit will be issued upon arrival. But if you will transit in other cities, you have to apply for a transit G visa in advance.