To meet the requirements of the Energy Efficiency Existing Ship Index (EEXI) and achieve the goal of energy saving and emission reduction, energy-saving devices are commonly installed on ships, such as the pre-swirl fairings in front of propellers. This device changes the direction of the water flow into the propeller, thereby reducing the rotational loss of the propeller and enhancing propulsion efficiency. This paper proposes an automatic optimization design method for the pre-swirl fairing in front of the propeller. The parametric deformation of the shroud is realized by the secondary development of 3D CAD software. The computational fluid dynamics (CFD) method is used to evaluate its performance, and the adaptive particle swarm optimization (APSO) algorithm is used to realize automatic optimization. The design and optimization of the pre-swirl fairing in front of the propeller of a bulk carrier are carried out. The results show that the energy-saving effect of the optimized energy-saving device can reach 4.18 %, which verifies the feasibility and effectiveness of the method proposed in this paper.