Abstract: In order to improve the accuracy of gas mass spectrometry analysis in online mass spectrometry detection, this article analyzes the composition of the online continuous dynamic sampling system.The results show that the adsorption effect of condensable gas in the drainage segment, the mass discrimination effect of the throttle segment, and the difference in the pumping speed of different gas components by molecular pump bring original errors to the mass spectrometry component analysis.According to the theory of molecular gas dynamics, this article defines the mass discrimination coefficient γ that characterizes the throttle segment and derives its relationship with the pumping speed ratio S_Cj/S_Ci of two gases by the molecular pump.This corrects the mass discrimination effect of the sampling system, which fundamentally improves the accuracy of mass spectrometry composition analysis.