Abstract: Helium mass spectrometer sniffing probe method is widely used in the process of the single point leak testing on the spacecraft. So it is important to study the uncertainty evaluation of this method. First,the method of uncertainty evaluation was studied based on the basic theory about uncertainty. Secondly,the detail evaluation steps were also given through a example. The presented evaluation method may provide a reference for evaluating the uncertainty about the total leak rate method of spacecraft and vacuum leak testing method.