Abstract: Vacuum system which contain of corrosive metearals is always strict for leakages. This paper reasearched the online leak detecting methods of vacuum system which contain of corrosive metearals. It analyzed relatively leak detecting methods， supplied a suitable way. First，dealt with corrosive metearals， elected suitable leak detecting steps， made the leak detector fulfilled with its working condition， then used helium cumulated method to acquire leakage rates. The result indicate that the method could detect the vacuum system online leakage exactly and availability. The study provide an assistant technique for the online leakage detecting of vacuum system which contain corrosive metearals.