The flexible gear is the key parts of harmonic gear reducers,and its performance directly determine the overall condition of harmonic drives. In order to seek the basic law of influence of flexible gears wall thickness on its performance to make use of the law,the influences of flexible gears wall thickness on stress and deformation of the flexible gears are simulated and analyzed by ANSYS Workbench software under no-load and load conditions. The results show that,the maximum stress of the flexible gear increases and the maximum deformation decreases with the increase of the wall thickness under no-load condition. With the increase of the wall thickness,under the load condition,the maximum stress decreases overall and the maximum deformation decreases first and then tends to be gentle. Under the same wall thickness,with the increase of the load,the maximum stress and the maximum deformation both enhance and the load is more sensitive to the deformation in the places whose wall thickness are relatively thinner. Under the same conditions,the stress of flexible gear with bottom modification is smaller. This law can provide some reference for researchers.