As a key equipment in underwater pressurization technology， the underwater helical axial flow mixing pump is widely used in the development of offshore oil and gas fields. How to further enhance its pressurization performance has attracted the attention of researchers. This study adopts a method combining orthogonal experimental design and numerical simulation to optimize 5 key structural parameters of the helical axial flow pump impeller， aiming to improve the pressurization performance of the mixing pump. Using Fluent software and the standard SST k-ω turbulence model， numerical simulations are conducted on a singlestage compression unit of a helical axial flow pump with an impeller shaft diameter of 350 mm. The influence of five different structural parameters of the impeller on the pressurization performance is studied， and the optimal parameter combination is determined. The results show that under the operating conditions of a flow rate of 500 m3/h and a speed of 4500 r/min， the pressurization performance is optimal for a compression unit with three blades， a blade wrap angle of 130°， a blade thickness of 6 mm， and inlet and outlet angles of 6°， achieving 2.02 MPa， which is a 22% improvement in pressurization compared to the initial structure. Finally， numerical simulations are carried out on the optimized threestage mixing pump impeller under different operating conditions to predict the pressurization effect. The research results provide a theoretical basis for the design and optimization of underwater helical axial flow mixing pumps.