The work aims to complete an edge folding action on the inner box forming machine, to fit the inner box strip of certain carton to the surface paper accurately. Through the study on motion characteristics of the edge folding device with connecting rod mechanism, the designed method was analyzed and optimized. The root mean square between the expected trajectory and the actual trajectory was taken as the objective function of the optimization, and the optimal size under the limited conditions was searched by the Matlab. The corresponding model was established in the Adams to simulate the motion trajectory curve of the simulated connecting rod. Finally, through the comparison between the actual design trajectory and the virtual simulation trajectory, it was found that the maximum error between the virtual trajectory curve and the designed curve was 0.36 mm. The work is in line with the actual needs of paper folding in actual production, verifies the correctness of the optimization design results, and provides a certain reference for the carton forming industry.