Abstract: To study the influence of ion beam perveance condition on the grids erosion velocity for 30 cm diameter ion thruster, we established a beam perveance model and calculated the grids erosion velocity caused by CEX (charge exchange) ions by PIC-MCC method, and then compared and analyzed the calculation results with 1500 h short time life test results. The results show that under the normal beam perveance condition, the mass erosion velocity of the accelerator grid and the decelerator grid are (1.11−1.72)×10⁻¹⁵ kg/s and (1.22−1.26)×10⁻¹⁷ kg/s in 3 kW and 5 kW working modes, respectively. Under 5 kW working mode, when the upstream plasma density of the screen grid reaches 4.03×10¹⁷ m⁻³, the beam is under perveance condition, and the maximum ion erosion velocity of the accelerator grid and the decelerator grid is about 4.33×10⁻¹⁵ kg/s and 4.02×10⁻¹⁵ kg/s respectively. Under 3 kW working mode, when the upstream plasma density of the screen grid reaches 0.22×10¹⁷ m⁻³, the beam is in over perveance condition. Meanwhile, the maximum ion erosion velocity of the accelerator grid and the decelerator grid is about 3.24×10⁻¹⁵ kg/s and 5.01×10⁻¹⁵ kg/s respectively. The life test results show that the calculation value of mass erosion velocity of the accelerator grid hole has a small error to the test value. However, the calculation results of erosion velocity of the decelerator grid hole differ greatly from the test results, which is mainly because of the direct bombardment of the beam ions on the decelerator grid hole. From the current research conclusions, it is considered that the variable aperture design for the screen grid hole is an effective measure to reduce the erosion velocity of the accelerator grid hole and the decelerator grid hole caused by CEX ions when the beam is in under or over perveance condition. In addition, variable aperture design of the grids can significantly improve the working life of the thruster.