Abstract: With the increase in power and miniaturization of TWT, the distribution of collector temperature and the cooling method have great effect on operation of TWT. The thermal performance of TWT collector is explored by simulation using ANSYS package. The ways of applying boundary condition that affect the distribution of collector temperature are compared. An overview of the thermal behavior for collectors with different structure and different cooling methods，such as free convection, forced convection, single and double channel water-cooling, etc., is given. The result estimated by simulation is consistent with the experiment and proves that the model and method employed are suitable.