Due to the complex geometry of free-form surfaces, the generating optimization trajectories of spray gun satisfy the requirement of uniformity paint became a challenge. A quadratic function of the paint deposition rate on a plane was proposed according to the experimental data, and a model of paint deposition rate on a free-form surface was established. The point cloud model was obtained directly by scanning the surface of workpiece, and the position and pose of spray gun was obtained by point cloud slicing technique. The change of the surface curvature caused non-uniform paint deposition on freeform surface. An algorithm of variable spray speed optimization was established to compensate for the curvature change and improve the uniformity of paint deposition along passes. An algorithm for selecting the spacing between the passes was established to improve the deposition uniformity vertical to passes, and to reduce cycle time and paint waste. Finally, the simulation and experimental results illustrated the feasibility and availability of these optimization algorithms. 