Abstract: Grid assembly is the core component of ion thruster beam extraction,acceleration and focusing,and its thermal deformation in the process of thruster operation is one of the key factors affecting the performance and service life of ion thruster.In this paper,the structural equivalent model of the grid assembly is established,and the temperature distri-bution of the grid assembly is simulated.The finite element software is used to calculate and draw the change curve of ther-mal deformation displacement of the grid assembly along radial coordinates at different positions on the grid surface at the same time.The change trend of grid spacing between screen grid-accelerating grid and accelerating-decelerating grid at the center of the grid assembly during the starting process is studied,and the simulation model is verified by non-contact opti-cal measurement method.The experimental results are in good agreement with the simulation results.To some extent,it re-flects the relationship between the hot grid gap and the cold grid gap of the grid assembly,which is helpful for the future research of grid sputtering corrosion,grid deformation and unexpected breakdown.