Aiming at the complex assembly deformation and stress distribution of cup shaped harmonic reducers，a finite element analysis model was established based on ANSYS software to analyze the stress and deformation laws of the harmonic reducer during assembly and loading.The research results show that the wave generator and the flexible wheel assembly causes varying degrees of tilting of the flexible wheel and bearing outer ring; after the assembly of the rigid wheel and flexible wheel,the maximum radial deformation of the flexible wheel and bearing outer ring at the long axis position is reduced by 14.1% and 9.1%,respectively; as the load increases,the stress growth trend of the flexible wheel shows an increasing slope;after 153 N·m,the stress of the flexible wheel accelerates,with a slope of approximately 0.354; the deformation of the flexible wheel assembly is measured using a 3D strain measurement system,and the experimental and simulation results are basically consistent.The research results indicate that flexible wheels,bearings,and rigid wheels have a significant impact on the stress and deformation distribution of harmonic reducers,providing data support for the design,use,and performance testing of harmonic reducers.