Addressing the issues of surface machining quality and residual stress in small impellers, the outward opening integral small impeller was selected as the key research object, and the main evaluation indicators of the surface quality of the experiment were set as the surface roughness and residual stress. The finite element simulation technology was used to analyze how the process parameters can affect the residual stress and outer surface roughness of the small impeller. After obtaining the results, the genetic algorithm was used to optimize it to obtain the optimal combination of process parameters. The surface roughness is reduced by 34.2%, and the residual stress is reduced by 28.6%, and at the same time, proved the feasibility of the optimization of the process parameters. The numerical control machining test of the small impeller was carried out to verify the feasibility and accuracy of the process parameter optimization.