In order to improve the design method of the blade and ventilation efficiency of the SWF type fan, this research used numerical simulation and the FLUENT software to analyze the internal flow field of the mixed fan and obtains the change rule of internal stress field and velocity field. Then, with the help of the FluidStructure coupling principle and the ANSYS Workbench, we added the stress in the flow field to the solid model. And the stress and displacement of the fan were obtained. Finally, by changing flow velocity, many sets of different stress and efficiency were obtained, and the efficiency curves of the fan was fitted by MATLAB. The results show that stress decreased gradually from root to top of the blade, and the maximum stress appeared at root of blade. The displacement increased gradually from root to top of the blade, and the maximum displacement appeared at top of blade. The highest efficiency was at the velocity of 6.8 m/s.