Abstract: Based on the Hertz contact theory and elastohydrodynamic lubrication theory, this paper focuses on the FB815-flexible ball bearing of harmonic reducer and proposes a mixed lubrication model to study the tribological performance of the contact region between ball and inner raceway in flexible ball bearing.The distribution of dangerous location was found by obtaining the film thickness, pressure, film thickness ratio and other lubrication parameters of bearing loading region at rated working condition.Then the effects of load, speed, temperature and other related affecting factors on the mixed lubrication performance of dangerous location were studied. The results show that appropriately increased rotation speed and decreased temperature, in a certain range, effectively reduced fatigue pitting and improved the reliability and service life of flexible ball bearing.