Abstract: Grids system electron backstreaming is one of key failure models for ion thruster.This paper that is based on the 20 cm Xe ion thruster operation data and considered the failure mechanism of ion thruster grids system electron backsteraming,evaluate the effect of electron backstreaming on ion thruster for operating on ground and space.The result indicated that the life of 20 cm Xe ion thruster while appear electron backstreaming are 6 600 h and 17 000 h for operating on ground and space respectively.