Abstract: The working stress and life of the flexible wheel determine the transmission performance of the whole harmonic reducer. The research on the stress distribution and fatigue strength of the flexible wheel is conducive to improving the accuracy of harmonic transmission and the service life of the flexible wheel. The peak stress and the fatigue safety factor of the cup type flexible wheel of a harmonic gear reducer under no load are calculated theoretically. The accuracy of the calculation results is verified by Inventor modeling and ANSYS Workbench simulation software, and the law of the maximum equivalent force and deformation of the flexible wheel changing with the load is obtained. The results show that the maximum deformation of the flexible wheel is in the long and short axis area. The maximum equivalent stress of the flexible wheel is in the transition part between the ring gear and the cylinder and the transition part between the flange and the cylinder. The increase of the torque has little effect on the maximum displacement of the flexible wheel, and the maximum stress increases with the increase of the load, and the optimal working section of the flexible wheel is the load less than 100 N. By inputting S-N curve of flexible wheel material, the cloud chart and change curve chart of safety coefficient of flexible wheel under different loads are obtained, which can confirm that the flexible wheel is prone to fatigue fracture when it is subjected to a torque about 110 N.