At present, the research goal of triplescrew pump is to achieve high speed, high pressure and large flow. The important way to improve the working pressure of triplescrew pump is to improve the design and processing accuracy of the screw profile, and strictly control the transmission clearance to reduce the internal leakage of the pump. The main and driven screw rotor profiles were generated by numerical calculation method and verified by programming in MATLAB software. The threedimensional model of the main and driven screw was established in UG software. The simulation analysis was carried out in Fluent software. The flow channel pressure under different center distance and different top clearance of the main screw and the driven screw and the distribution law of the inner flow field pressure and the flow line corresponding to the position of the screw rotation angle were obtained.The simulation results show that when the tip clearance increases from 0.1 mm to 0.2 and 03 mm, the pressure decreases by 3.85% and 81% respectively along the axial distance from 80 to 100 mm to the screw end face, while the pressure decreases by 16.9%, 16.6% and 15.4% respectively under different pressure differences, and the greater the pressure difference, the greater the leakage.The pressure of pump chamber fluctuates with the increase of center distance. When the center distance increases from 45 mm to 45.3 mm, the pressure value decreases by 10% as the output set pressure difference is 5 MPa, while the pressure value decreases by 9.7% and 9.6% respectively as the output set pressure difference is 4 MPa or 3 MPa.