Abstract: Ion thruster mainly has two grid optical system configuration modes:convex and concave grid.In order to study the influence of grid optical system configuration modes on the operating characteristics of ion thruster,combined with the performance tests of LIPS-100 ion thruster developed by Lanzhou Institute of Physics,which operated in 20mN thrust,various operating characteristics of the concave grid optical system including the discharge loss,ion beam current density distribution,and start-up characteristic at cryogenic temperature condition were verified by expe-riments comparing with the convex grid optical system.Comparisons illustrate that the concave grid optical system confi-guration decreases the discharge feature size and increases thermal grid spacing,resulting in the thruster can be started-up with full power in 10s at-90 ℃ cryogenic temperature condition,but the discharge loss is increased by 5.3%.Concurrently,the extracted ions of the concave grid are more focused,which reduces the beam divergence angle by 18.6%,but the ion beam flatness is decreased by 19.6%.The study can provide approach for the selection and optimization of grid optical system configura-tion for ion thruster.