Abstract: According to the uniform load-deflection behavior of the pressure sensing diaphragm of capacitive diaphragm vacuum gauge under pre-tension conditions, Von Karman equation and the Beams equation are selected as the theoretical model of the pressure sensing diaphragm. And the nonlinear finite element simulation analysis is carried out in combination with the static module in ANSYS Workbench software. The results show that the pre-tension has a significant effect on the deflection of the pressure sensing diaphragm. The deflection of the diaphragm decreases with the increase of the pre-tension. With the increase of the uniform load and the pre-tension, the decrease of deflection of the pressure sensing diaphragm is weakened. Under the same uniform load, the greater the pre-tension, the greater the influence ratio. When the uniform load increases and the deflection of the pressure sensing diaphragm increases, the deflection caused by the pre-tension is decreasing, and the influence ratio is gradually decreased. When the pressure sensing diaphragm is initially deformed by the 1 Pa uniform load, the pre-tension of 13 MPa has a 93% influence on the deflection of the diaphragm; when the uniform load exceeds 800 Pa, the deflection caused by the pre-tension is less than 35% of the deflection of the entire pressure sensing diaphragm; The uniform load is 1 000 Pa, and the pre-stress is 7 MPa, the influence ratio is 17.9%. The simulation results are verified by using the real capacitive diaphragm vacuum gauge.