We attempt to resolve the spraying trajectory planning efficiency and the thickness uniformity problems for big curvature conical surface in complex curved surfaces. By experimental data, the coating growth rate model is obtained and we analyzed the applications of the model on conical surface. Based on the characteristics of conical surface is the regular surfaces, we planned the spray gun trajectory on this surface, and used the methods of adjust the spray radius and track section to discussed the calculation method of the coating thickness and optimization of correlation parameter. Taking car bumper for example, we studied the spray trajectory optimization on the juncture of conical surface and plane. Simulation results show that, our method can effectively increase the efficiency of spray trajectory planning under the premise of ensuring the thickness uniformity, the spray velocity show the non-linear variations with spacing distance and others show the linear variations, the uniformity of coating thickness meets the quality request on the juncture of conical surface and plane.