We attempt to resolve the spray trajectory planning efficiency and the coating thickness uniformity for big curvature surface on complex curved surfaces. The least square method was proposed for spray partition of complex curved surface based on topology partition. First, the big curvature surface was extracted from complex curved surfaces. Then, the big curvature surface was fitted into the natural quadric surface based on least square method and the fitting algorithm was given. Simulation results show that, the fitting algorithm is feasible, and this method can effectively reduce the number of patches, which can improve the spray trajectory planning efficiency and the coating thickness uniformity.