This paper takes the nitrogen pressurizer system of small reactor as the research object, and establishes the reactor primary circuit and nitrogen pressurizer system models through the one-dimensional system simulation program LOCUST. Through the Latin hypercube sampling method, factors such as the inner diameter of the wave pipe, the inner diameter of the gas tank branch pipe, the gas–water temperature, the gas–water ratio, the pressurizer volume and the auxiliary gas tank volume are comprehensively considered. The optimal configuration scheme of nitrogen pressurizer system parameters is determined by the rising power and falling power conditions. The results show that the pressure amplitude of the optimal regulator decreases by 15.58% and 10.93% respectively compared with that of the original regulator. Then the nitrogen pressurizer control system model is established, and the transient response characteristics of the nitrogen pressurizer system under different transient conditions are analyzed. Compared with steam pressurizer, it is found that the pressure overshoot of nitrogen pressurizer decreases obviously under the condition of turbine trip and load rejection.