Abstract: Abstract: Objectives This paper aims to study the impact of propeller boss cap fins on the performance of ship propulsion devices and its optimization, verify the energy-saving effect of propeller boss cap fins, and provide the optimal design parameters to achieve the goal of reducing energy consumption and improving navigation efficiency. Methods This article analyzes the energy-saving mechanism of installing propeller boss cap fins on propellers through the method of CFD steady state calculation, using SST k- ω Turbulence model for calculation. Based on the study of its mechanism, the influence law of parameters such as the installation angle, axial position, and diameter of the propeller boss cap fins on the overall hydrodynamic performance is analyzed. Results The results show that installing the propeller boss cap fins can weaken the hub vortex strength, recover wake energy, eliminate the low-pressure zone on the propeller boss cap fins, and generate negative torque on the fin blade, so as to improve the efficiency. Research has shown that within the range of studied parameters, when the installation angle is close to the pitch angle at the root of the propeller blade, the energy saving effect is best; The increase in axial position can improve the energy-saving effect to a certain extent, but when it is increased to a certain distance, the propulsion efficiency under partial acceleration coefficient will decrease; When the diameter of the propeller boss cap fins is 0.26D, it has a higher energy-saving effect. Conclusions The results of this study can provide reference for the energy-saving effect of propeller boss cap fins in the future.