Abstract: The classical control method is usually hard to ensure the thermal power tracking accuracy, because the nuclear reactor system is a complex nonlinear system with uncertain parameters and disturbances. In the paper, a sort of non parameter model is constructed with the open loop impulse response of the system. Furthermore, a sort of thermal power tracking digital control law is presented using the multi step model algorithmic control principle. The control method presented in the paper has good tracking performance and robustness. It can work despite the existence of unmeasurable disturbances. The simulation experiment testifies the correctness and effectiveness of the method. The high accuracy matching between the thermal power and the referenced load is achieved.