Abstract: In this paper, the internal flow characteristics of the double-helix axial flow pump under different axial clearances of the rotor are studied by changing the axial clearance between the two spiral rotors (1, 5, 10 mm). Based on the CFD simulation platform, the immersed solid method was used. The N-S equation and the standard k - ε turbulence model were used to numerically simulate the transient characteristics under different axial clearances and different working conditions, and the transient flow characteristics of each flow component of the double-helix pump under different rotor clearances were obtained. The results show that the head of the pump is the highest when the rotor clearance is 1 mm, and the head of the pump decreases with the increase of the rotor clearance (5 mm and 10 mm). The booster performance of the pump is the best under the 1 mm gap, but the fluid has obvious negative pressure phenomenon when it just enters the rotor domain. After the gap increases, the anti-blocking ability in the rotor is enhanced and the negative pressure phenomenon is improved. The main leakage area of the double helical axial flow pump is in the rotor meshing area. With the increase of the axial clearance of the rotor, the speed of the meshing area increases, and the leakage is obvious. The head of the double screw pump is inversely proportional to the flow rate. With the increase of the design flow rate, and the head of the three gap pumps gradually decreases.