In this paper, a fast finite control set model predict control (FCS-MPC) strategy is implemented in cascaded H-bridge Static Synchronous Compensator (STATCOM). A universal calculation model of IGBT and the anti-parallel diode dissipation power in MATLAB/Simulink is built. Through the system simulation, the parameters, such as the withstand voltage, the current through the device, the junction temperature of the devices, and so on, are obtained at action stations (turn-on, turn-off, conduction or blocking). Thermal resistance network is used to calculate the junction temperature and dissipation power. Under the steady state, the average power loss and the maximum junction temperature of each device are obtained. The validity and accuracy of the method have been validated by the simulation and experimental results. The quantitative analysis of the effects of power grid voltage, control time and switching loss weight coefficient on the loss value of each device are offered, which is an important reference value for the thermal design of the equipment.