The principle of catering tray experiment is based on the microbial growth of food in different environments. Catering tray experiment is a method to test food safety. In the experiment, a certain number of colonies were coated on a tray and then cultured under different temperature and humidity conditions. After a certain period of time, observe the growth of colonies on the tray and evaluate the food hygiene. By this method, it can be judged whether there is the risk of pollution and bacterial growth during the storage and transportation of food in different environments.