In order to solve the unstable quality，lower efficiency and harsh working envirnment of hand-sanding for high speed train body in white，robot-sanding and constant force control technology were used to optimize the sanding process of putty. By using orthogonal experimental design and surface smoothness and roughness as indicators，the specific parameters of sanding process was investigated. The results showed that the quality of putty sanding could be improved by selecting proper mesh number of sand paper，applied force and moving speed. Taking the whole-body surface smoothness as indicator，by optimizing the sanding path，frequency and sandingmode，a high speed train body in white surface with good smoothness can be obtained.