Abstract: Considering that the gear is usually in mixed lubrication state during transmission, the calculation method of friction coefficient of boundary lubrication and elastohydrodynamic lubrication, combined with the calculation method of rough peak contact, is used to establish the calculation model of friction coefficient of mixed lubrication state. The minimum oil film thickness between tooth surfaces was analyzed and compared with the classical literature to verify the correctness and reliability of the calculation model in this paper. The distribution of the minimum oil film thickness along the meshing line was used to determine the poorly lubricated area. The lubrication state of gears under different working conditions was studied by calculating the film thickness ratio based on the minimum oil film thickness at the starting point of gear meshing. According to the gear meshing principle and heat transfer theory, the specific distribution of frictional heat flux on the meshing line was obtained, and the difference of heat flux between the modified gear and the standard gear was compared. In order to improve the calculation accuracy of the heat dissipation model, the thermal property parameters of oil and gas mixture were used as the lubricating medium for convection heat transfer. The convection heat transfer coefficients of the gear tooth meshing surface, end surface, root and top surface were calculated. Meanwhile, the convection heat transfer coefficients of the pitch circle and the different meshing points of the meshing line were calculated respectively, and the influence of different loading modes of convection heat transfer on the temperature field was discussed. The contact surface of gear was cut in finite element software with the idea of differentiation, and a single tooth finite element thermal analysis model was built to reveal the influence of different number of strips area division, different loading modes of convective heat transfer, different speed, torque, tooth profile modification and roughness on the temperature field. The results showed that the minimum oil film thickness was not evenly distributed on the meshing line, the oil film thickness at the beginning meshing point of the drive wheel and the single tooth meshing zone was small, and the lubrication was relatively poor. In order to obtain more accurate results of temperature field distribution, the influence of different number of bars on temperature field was analyzed. It was found that the number of strip division had a certain influence on the temperature accuracy. When the number of strip area division was 50, the maximum and minimum temperature of the tooth surface tended to be stable. The convection heat transfer loading mode had little effect on temperature. The temperature of the tooth surface increased gradually with the increase of speed and torque, and the average temperature growth rate decreased gradually with the increase of speed and torque. The influence of torque on the temperature rise of the tooth surface was greater than that of speed. The tooth profile modification could weaken the impact of load in and out of the tooth surface and make the temperature distribution of the tooth surface more uniform. By modifying the tooth profile, the temperature of the driving wheel was reduced from 69.06 ℃ to 67.06 ℃, with a decrease of 2.9%. The lower the roughness was, the closer it was to the elastohydrodynamic lubrication state. The temperature of the tooth body was proportional to the roughness. As the roughness decreased, the temperature also decreased.