In view of the main steam temperature control of the secondary reheating unit, the controlled object usually has severe nonlinearity, hysteresis, and timevarying characteristics.It is difficult to obtain satisfactory dynamic response characteristics using traditional cascade PID control.By analyzing the thermal system of the secondary reheating unit, an optimized control method for the main steam temperature based on particle swarm optimization was proposed to realize the rapid optimization of the PID controller parameters of the main loop of the cascade control system.Based on the Matlab / Simulink platform, step response experiments were performed on the controlled object model.The simulation results show that the control performance of the regulation loop after particle swarm algorithm optimization is significantly improved compared with the ZN tuning method.The optimized control method not only retains the advantages of strong antiinterference ability of the cascade control system, but also effectively resolves the contradiction between stability and accuracy in the main steam temperature control system, and enhances the system’s adaptability to uncertain factors，which have a certain guiding significance for engineering applications.