Abstract: For the evaluation of the sealing performance of vacuum shells,a comparison method of leak rate based on the standard leak is proposed,which specifically includes the dynamic comparison method and the static cumulative comparison method.The ion currents generated by the outflowing gas of the standard leak and the sealed shell are compared by a quadrupole mass spectrometer (QMS).Using the known leak rate of the standard leak and the linear extrapolation of the ion response by the QMS,the shell’s leak rate is calculated.A device for measuring the leak rate of the seal is developed,which has a limit vacuum pressure down to 10^-7Pa,a leak rate measurement range of 10^-7-10^-14Pa·m³/s.It can be used for leak rate testing of various seals with detection interfaces.The leak rate of a stainless steel knife-edge seal was measured by the two methods.It is indicated that the dynamic comparison method has a large test error for this sample,and it is advised that the sealed shell with an extremely low leak rate,such as lower than 10^-11Pa·m³/s,is more suitable to be tested by the static cumulative comparison method.