Abstract: As an important component of the helium mass spectrometer leak detector,the geometric parameters of the composite molecular pump not only affect the pumping performance,but also affect the detection performance of the leak detector.Based on the basic theory of molecular pump,this paper establishes the calculation model of the traction stage of the composite molecular pump.By changing the spiral angle,the traction groove depth and the gap between the rotor and stator,the pumping performance of the traction stage of the composite molecular pump for the two gases involved in the helium mass spectrometer leak detector under different working conditions is calculated respectively,The influence of trac-tion stage parameters of composite molecular pump on the detection performance of helium mass spectrometer leak detec-tor was studied.The results show that the sensitivity of helium mass spectrometer leak detector increases first and then de-creases with the increase of spiral angle.The sensitivity of helium mass spectrometer leak detector increases first and then decreases with the increase of traction groove depth.Increasing the gap between rotor and stator is not conducive to the im-provement of the sensitivity of helium mass spectrometer leak detector.When the spiral angle is 22°,the traction groove depth is 2.5 mm and the gap between rotor and stator is 0.3 mm,the helium mass spectrometer leak detector has high sen-sitivity,and the traction stage of the composite molecular pump has reliable performance and safe structure.