Abstract: In order to study the effect of the clearance of rotor-stator cascade on the pressure fluctuation in the secondary circuit coolant pump for sodium-cooled fast reactors, the unsteady numerical simulation method based on SST k-ω turbulence model was applied on five model pumps with different clearance of rotor-stator cascade. The relative clearance of rotor-stator cascade of five model pumps were 3.030%, 4.545%, 6.060%, 7.575% and 9.090%, respectively. The characteristics of pressure fluctuation and radial force on the rotor were obtained by unsteady numerical simulation, and the comparison and analysis were made. The results show that both of the head and efficiency of the pump with a relative clearance of rotor-stator cascade of 7.575% are better than those of any other four model pumps. The main frequency of the pressure fluctuation of each measuring point in the guide vane passage is the impeller blade passing frequency, and the amplitude at the impeller blade passing frequency of the pressure fluctuation of each measuring point gradually decreases along the guide vane inlet to the outlet direction. With the increasing of the clearance of rotor-stator cascade, the amplitude at the impeller blade passing frequency of the pressure fluctuation at each measuring point and the radial force fluctuation of the rotor are gradually reduced, and the high frequency fluctuation component decreases. Meanwhile, the fluctuation of the magnitude and direction of the radial force vector of the rotor is gradually weakened.