At present, the general steps for heat sink design of power semiconductor devices are: First, calculate the allowable thermal resistance of the heat sink, then select the corresponding heat sink according to the thermal resistance, and finally test whether the junction temperature of the power device is allowable. Inside. Since there are many approximations to the calculation of the thermal resistance, the resulting thermal resistance is just the average thermal resistance of the heat sink. Therefore, the temperature distribution diagram on the radiator cannot be obtained and the result is lack of intuitiveness. In addition, the heat resistance Rthsa from the surface to the environment of different heat sinks of different materials and shapes varies considerably, so this increases the difficulty of calculating the total heat resistance Rth. The literature took into account the effect of temperature on various losses. Using the equivalent circuit of thermal resistance, the general formula for the temperature of each point of the radiator system was deduced. The method is cumbersome and the practicality is not well.In order to simulate on thermal field of air-cooling radiation，it is necessary to calculate the value of the convection heat transfer coefficient. According to the theory of thermal conduction，the paper establishes power semiconductor device and its physical model of air-cooling radiation，provides the formula of convection heat transfer coefficient and its parameters table of dry air on different conditions. It provides flow chart of convection heat transfer coefficient on simulation. The simulation and experiment verify the calculation formula of convection heat transfer coefficient and the validity of adjustment method.