The high-speed train gear box thermal network model was established by converting the gearbox components into temperature nodes, and the heat balance temperature was calculated by calculating the thermal power loss and the thermal resistance in the heat transfer process with Matlab. The influence of gear box input speed, viscosity of lubricating oil and thermal conductivity of box material on the thermal balance temperature of gear box key parts were analyzed. The results showed that the thermal balance temperature of the gearbox bearings, gears and lubricating oil of high-speed train increases with the increase of the gearbox input speed and the viscosity of the lubricating oil, while decreases with the increase of the thermal conductivity of the box.