In order to achieve large complex surface spraying trajectory planning,a coating thickness model-based spray trajectory planning method for high-speed railway car-body-in-white robot was proposed. Based on the elliptic double β distribution model of static coating thickness,the distribution rule of the cumulative coating thickness was analyzed,and a new index RU for evaluating the relative inhomogeneity was proposed. Based on RU index,the consistency of coating thickness was ensured by the way of track overlap.Then,the division of spraying area was realized through the segmentation and merging of curved surface.At the same time,the robot spraying path point space coordinate information was determined based on the bounding box method.The experimental results show that the trajectory planning method based on the coating thickness model can effectively guarantee the uniformity of the spraying effect.It is successfully applied to the robot spraying process of high-speed railway body,the spraying quality and efficiency are greatly improved.