To provide a theoretical basis for accelerated life test and support for product optimization design, the tooth profile equation of the flexible wheel and rigid wheel is derived based on envelope theory. The load condition, curvature radius and volume absorption speed of the meshing area are analyzed. Considering the macroscopic geometry of contact area and the real surface roughness of meshing area, a mixed lubrication model of the flexible wheel and rigid wheel was established. The influence of speed and temperature on lubrication performance was studied by analyzing the film thickness ratio, friction coefficient and other related affecting factors. The results show that, when the speed is higher, the average film thickness and film thickness ratio are greater, the contact load ratio and the contact area ratio are smaller and the lubrication performance is better. When the speed is higher than 2 200 r/min, the meshing zone turns from boundary lubrication to mixed lubrication, the contact load ratio and the contact area ratio are reduced by more than 90%, the friction coefficient is reduced by more than half compared to 50 r/min. Controlling the speed over 2 200 r/min is helpful to improve the lubrication condition. When the temperature of the meshing zone increases, the average film thickness and film thickness ratio decrease and the contact load ratio and the contact area ratio increase, the lubrication condition deteriorates. When the temperature is at 60 ℃, the friction coefficient, contact load ratio and contact area ratio are more than doubled compared to that at 10 ℃. The harmonic reducer's working temperature should be controlled below 60 ℃ strictly.