There are large prestress and predeformation when the flexible bearing of the harmonic reducer is fitted to the elliptical cam of the wave generator.To study the effect of prestress and predeformation,the multibody contact model were built by ANSYS Workbench,considering the predeformation and prestress of inner and outer rings of the flexible preassembled bearing.The deformation,stress and load distribution of the flexible inner and outer bearing rings were obtained under practical working condition.The analysis result shows that the equivalent stress of the inner and outer ring is mainly determined by the circumferential stress.The maximum equivalent stress and the maximum radial stress of the inner and outer ring occur in the contact zone between the ball and the inner and outer rolling track at the major axis.According to LP theory,the fatigue life of flexible bearing was calculated.It is shown that the fatigue life of flexible bearing is reduced by 30% in the case of prestress.The research results provide the theoretical reference and guidance for the design and prediction the fatigue life of flexible bearing.