The work aims to analyze the behavior of internal flow fields when the helical rotor pump (HRP) is operating at high speeds and high pressures, which provides theoretical basis for the structure optimization of such HRP. The 3D model of HRP at high speeds and high pressures was established with SolidWorks. FLUENT was applied to simulate the internal flow fields of HRP operating at high speeds and high pressures to obtain the contours of pressure. The influences of speed on the maximum pressure and the maximum negative pressure of oil film with and without cavitation were compared. Cavitation had little effect on the meshing pressure in the high-pressure area. The maximum pressure and the maximum negative pressure at the gear meshing part and the occupation of air in the hydraulic oil were increased with the increase in the rotation speed. When the speed was 12 000 r/min, the air occupation was up to 12.81% and the pressure at the meshing part could reach up to 37.5 MPa, which was 1.5 times the size of pressure at the oil outlet. The cavitation prevents the leakage of partial gear tip clearance, which has positive significance for the improvement of rotor stability. The maximum pressure appears in the area where the HRP rotor meshes, which causes the rotor to generate dramatic vibration and reduces the HRP stability.