The work aims to realize automatic and efficient coating operation on the packaging production line, establish a paint film thickness distribution model on the surface of the workpiece to be sprayed, optimize the spraying trajectory, solve the best feed speed of the workpiece to be sprayed and the rotation speed of the automatic rotary sprayer, and realize the optimization of the spraying trajectory of the automatic rotary sprayer. Firstly, the experimental data on the thickness of the paint film were obtained by the automatic rotary sprayer. The experimental data were characterized by the β-distribution model. Key parameters of the β-distribution model were fitted by the Matlab genetic algorithm toolbox. The spraying trajectory equation was determined according to automatic rotary sprayer spraying process. On this basis, the film thickness lap model was established. The best feed speed and the rotation speed of the sprayer were solved through the NSGA-Ⅱ algorithm. According to optimization with the NSGA-Ⅱ algorithm, the feed speed of the workpiece to be sprayed was 428.849 mm/s, the rotation speed of the sprayer was 6.22 rad/s, the spraying time was 6.995 s. The film thickness model of the sprayed surface can accurately reflect the actual spraying situation of the sprayed surface of the workpiece, and can reasonably optimize the spraying trajectory of the automatic rotary sprayer. It lays a foundation for realizing automatic spraying operations in packaging.