In view of various factors caused by the conventional test method for the main characteristics of vacuum generator, such as manpower, long time cost and big energy consumption, a new flowrate characteristics detection method based on isothermal chambers was put forward. According to the analysis of the testing principle, a new pilot system was made. Through the trial by using the new test method, practical tests were compared on several vacuum generators. Experimental results show that it has the advantages of less manpower, shorter time and significantly reduce for energy consumption. Compared to conventional method, the isothermal method reduces the air supply by 13%～81% and time cost by 17%～76%.