Abstract: Abstract: With the wide application of the rotary lobe pump, the rotary lobe pump rotor presents the development trend of being multi-leaf and spiral. In order to elucidate the influence of rotor spiral angle on the flow characteristics in the rotor cavity of rotary lobe pump, and reveal the quantitative relationship between the spiral angle and the characteristic curve of the lobe pump, based on FLUENT dynamic mesh and Renormalization Group k-ε turbulence model, the numerical calculation of 3D (three-dimensional) transient flow in the rotor cavity of rotary lobe pump is carried out. The internal flow characteristics in the rotor cavity of rotary lobe pump with 9 kinds of spiral angles are compared, and the mechanism of the influence of the spiral angle on the transient flow structure in the rotor cavity is revealed. Meanwhile, through theoretical calculation, numerical simulation and experimental verification, the comparative analysis of numerical prediction shows that the relative error is in the range of 2.5% - 5.7%, and the numerical simulation has higher accuracy. Research results prove that the periodic changes of the volume of the pump cavity at the high pressure side and the low pressure side make the velocity of the fluid in the gap region suddenly rise or fall, which is accompanied by the wall jet effect of the fluid in the clearance area. During the rotation of the rotor of the straight blade rotary lobe pump, the end wall secondary flow and the periodic flow pulsation appear at the outlet of the pump, the velocity increases abnormally at the rotor edge, and the local vortex structure appears in the rotor cavity. Compared with the rotor with straight blade, the spiral rotor can effectively suppress the secondary flow in the rotor cavity, the sudden change of the occurrence of the vortex structure and the velocity in the rotor clearance region. When the spiral angle is 45°-60°, the above flow phenomenon is obviously improved. The spiral angle has a significant effect on the flow pulsation at the outlet of the rotary lobe pump. Compared with the rotor with straight blades, the outlet flow rate of the spiral rotor decreases, and the amplitude of the outlet flow pulsation of the spiral rotor is also obviously decreased. When the spiral angle is 45°-60°, the flow pulsation amplitude at the outlet of the rotor cavity is only 60% of that of the rotor with straight blade, and the outlet flow rate of the pump reaches the maximum value, which is 97% of the outlet flow rate of the rotor, indicating that the optimum spiral angle of the rotor cavity of the rotary lobe pump is 45°-60°. Under the condition of variable rotational speed and variable outlet pressure, the performance tests of straight blade and rotary lobe pump with spiral angles of 45° and 60° are carried out because the axial leakage amount inside the rotor cavity is not taken into account in the numerical calculation. The numerical simulation and the experimental results are in good agreement with each other. At the same time, by using the theoretical calculation and the numerical calculation, the experiments are compared. The result shows that: because of the inlet and outlet pressure and the axial leakage are not considered in the theoretical calculation, there are some errors between them. But there is still a good degree of agreement. To sum up, through theoretical calculation, numerical simulation and mutual verification of experiments, it is shown that the rotary lobe pump has good performance when the spiral angle is 45°-60°, which provides a certain reference for the optimization design of rotary lobe pump rotor.