Abstract: A calibration method of partial pressure based on the combination of the static expansion vacuum basic standard and continuous expansion method is proposed, which solves the calibration problem of the minimum partial pressure below 10^-6 Pa. Based on the method, a new calibration device for the minimum partial pressure is developed. In the electron multiplier mode, the calibration experiment of quadrupole mass spectrometer (QMS) is carried out by injecting single gases. The experiment results show that the lower calibration limit of the partial pressure can be extended to 1×10^-9 Pa. And when the range of partial pressure calibration is 10^-5~10^-9 Pa, the corresponding uncertainty U_r=8.4% (k=2). The research ensures the accuracy of partial pressure measurement results when QMS is used in space exploration and other fields.