Abstract: The energy and density distribution of primary electron injected into discharge chamber are heavily influenced by the baffle aperture area,therefore it is a vital factor affected the performance of discharge chamber. For enhancing discharge stability,reducing anode voltage and discharge consumption,baffle aperture area of LIPS-100 ion thruster is optimized by tests under theory instruction. Ultimately,the optimized baffle aperture area is achieved by composite test with baffles and cathode magnetic poles with different diameter and its magnitude is diminished in 19% comparing before improvements. The test result shows that anode voltage is under 38 V about 4 V reduced,voltage oscillation declined to 6~15 V and discharge power consumption reduced about 10 W at 20mN operating point. The calculation shows that the lifetime of the screen grid of LIPS-100 ion thruster extends to 0.5 times more than before optimization for anode voltage reduced.