In the research into helium mass spectrometer leakage detection, a method for linearizability investigation has been put forward recently. Meanwhile, it has been demonstrated the rationality of the method through multiple tests based on the study in the principle of constant pumping speed of the mechanical pump in vacuum. The method realizes the control over the pressure through adjusting the leak detector inlet, so as to adjust gas flow rate in the leak detector. The concentration of helium in mixed gas is controlled via changing helium flow rate during leakage detection, so as to influence value display of the leak detector. With regard to test of linearity of the leak detector, a research has been conducted into relationship between the inlet pressure and output readings. The methodology of the research is characterized by simplicity, convenience, cost effective, and its test range covers most of the test leakageage rates in practice.