Abstract: One potential thruster failure mode is accelerator grid structural failure due to wear of the charge-exchange ions. The total mass loss when the accelerator grid was to be structure failure and accelerator grid life of 20 cm Xe ion thruster which was developed by Lanzhou Institute of Physics was calculation by the accelerator grid life model. The result of calculation was compared with the accelerator grid life of ground testing, and the 20 cm Xe accelerator grid life running in space was predicted by this model.