In order to predict temperature in a car, the thermal network method (TNM) was used to calculate the temperature when the car was parked or driven. Considering the solar radiation is the main factor which affects the temperature level in the car, TNM was used to calculate the temperature at each node after energy equations for all nodes have been established and solved, which is especially suitable for heat transfer problems dominated by thermal radiation. Empirical correlations were adopted to calculate the convection heat transfer between car surfaces and air. The established equations are non-linear, so the Newton iteration method was used to solve the equations. The calculation results are in consistent with the measured temperature, which indicates the effectiveness of TNM for the temperature prediction. Furthermore, the transmissivity of glass has obvious effect on the temperature level of the car. Without violating safety requirements, using glass with proper transmissivity can save energy for the car.