In order to provide the theoretical support for the gear strength improvement, tooth modification and design optimization, the change of temperature field of gear body under different speeds and torques conditions are analyzed. Taken the high-speed transmission shaft gear pairs of marine engineering lifting platform gear box unit as the object, based on the thermal theory, the heat flow density and convective heat transfer coefficient of different gear meshing surfaces are calculated. The large finite element software Ansys is used, the calculation results of the heat flow density and convective heat transfer coefficient are loaded into the Ansys as the boundary conditions, the steady-state thermal analysis is carried out on the gear, and the gears with different rotation speeds and torques under the normal conditions of steady temperature field are analyzed. The simulation results show that: under the normal steady-state conditions, the steady-state temperature field distribution of the driving wheel and slave wheel is similar, the highest temperature is distributed in the middle of the gear meshing surface, and the temperature gradually decreases towards the surrounding area; but the highest temperature of the driving wheel is higher than that of the slave wheel; the highest temperature of the driving wheel and slave wheel increases with the increase of the rotation speed or torque, and the corresponding lowest temperature also increases; the temperature distribution trend of the single tooth body of the driving wheel and slave wheel does not change with the change of rotation speed or torque; as the change of the gear temperature, under different torques and rotation speeds, the slope of the tooth surface temperature change is relatively stable, and there is no abrupt change; the temperature is concentrated on the tooth surface and diffused towards the gear axis, but the influence of temperature gradient change of the gear is small in the region 2.5 modulus away from the tooth root circle.