In order to solve the high temperature problem resulting from powerloss of automobile transmission when the transmission is working

the heat balance of the transmission is analyzed.The heat balance equations of the transmission are established by using thermal network method

the models for calculating the heat source power

thermal resistance and heat transfer coefficients are given

the temperature field distribution of transmission system is obtained through the calculation of heat balance equations by MATLAB program. The oil temperature test system is set up and the temperature of lubricant oil in transmission is tested and it is shows that the test results were basically agreement with the numerical results.It is shows that the heat balance model based on the thermal network method is correct and available.