Abstract: In the vacuum system,there are two important ways to seal the interface which are metal seal and rubber seal. The rubber seal belongs to self-tight seal,which is a kind of adaptable seals. So the rubber seal is used widely under the high vacuum. This paper discusses the deflated characteristics of Viton O-ring impact on analysis of trace impurity gases by using quadrupole mass spectrometer with closed ion source system. It is found that the Viton O-ring releases large amounts of oxygen. It's not suitable for using the rubber O-ring as seal device in the trace of impurity analysis system.