Abstract: The interface heat load characteristic of wet friction pair is an extremely important aspect in mechanical transmission system, and its abnormality will lead to component deformation. Considering the elastic-plastic deformation effect of the rough interface, a contact thermodynamic model was established based on elastohydrodynamic lubrication theory for wet friction pair under mixed lubrication condition. And some experiments were carried out to verify its correctness. According to the simulation results with rough contact area, local pressure distribution and local temperature distribution, the interface state change rule was analyzed under certain working conditions, and the effects of surface pressure and sliding speed on minute distribution of interface temperature field were explored. The results show that, with the increasing of surface pressure, the rough contact area and local intensity of pressure increase gradually, and the gap between the maximum temperature and the average temperature increases, indicating that the increasing pressure can intensify the pressure distribution polarization. With the increase of sliding velocity, the rough contact area and local pressure gradually decrease, while the maximum interface temperature increases rapidly at first and then decreases significantly. The extreme point appears in the range of 0.1 m/s~1.0 m/s.