Abstract: With the development of scientific research and production,the requirement of precision and long life of instruments is increasing.But the existing helium mass spectrometer leak detector can’t meet the requirements.The ultrahigh vacuum system material processing is used to reduce the background helium signal,non-evaporable getter pump is chosen to maintain static vacuum by selective pumping and static accumulation comparison method is used to amplify helium signal.The detection of 10^-13~10^-15 Pa·m³/s very low leakage rate is realized.The ultra sensitive leak detector and the very low gas flow calibration device designed according to the improved scheme provide reliability guarantee for the products of many companies in aerospace,nuclear industry and other industries.