Abstract: In the research of a high power amplifier,the work temperature of the power transistor is less than the rated temperature is ensure by the reasonable layout of each module and the correct choice of the cooling scheme. In this paper,the thermal design of the chassis is simulated and analyzed using Icepak,and the airflow pattern and parameters of the heat sink can be optimized according to the simulation results. Another thermal simulation analysis is made to compare with the former results. The simulation shows that the weight of the power amplifier reduces by 4.92 kg,while the case temperature falls by 2.2 ^o. It is validated the rationality of the airflow pattern and parameters of the heat sink.