<p>To optimize the aerodynamic performance of axial flow fans, this study employs the Computational Fluid Dynamics (CFD) method, taking the axial length and continuous curvature of the hub cap as the two parameters for investigation. The study systematically analyzes the effects of hub cap parameters on the airflow path, flow separation, vortex distribution, and aerodynamic performance inside the fan, while also conducting an in-depth investigation into the causes of vortex formation. The results show that increasing the axial length of the hub cap can significantly reduce the vortex area inside the impeller, decrease the pressure difference between the suction and pressure surfaces of the blades, and alleviate flow separation at the junction of the hub cap and hub profile. There exists an optimal axial length-beyond this length, further increasing the axial length has a negligible effect on improving fan performance. When the axial length is fixed, a well-designed arc-shaped hub cap surface can further enhance fan performance. Under the design flow rate of<i> Q</i> = 72,000 m³/h, the optimized hub cap increases the total pressure of the fan by approximately 100&#xa0;Pa. It improves the peak total pressure efficiency by approximately 16.5%. In addition, experiments verify the positive effect of the hub cap on fan efficiency. In summary, this study offers valuable guidance for the structural design of high-efficiency and high-pressure axial flow fans.</p>