In view of the limitations of domestic sweet potato transplanting mechanism on realizing horizontal transplanting trajectory, a sweet potato transplanting mechanism design method was proposed based on non-circular gears. Firstly, the requirements of horizontal transplantation agronomics were analyzed, the ideal trajectory, including seedling extraction, soiling, seedling throwing and other stages was planned, and nine key pose points were selected as the input parameters for solving the 2R chain opening mechanism. The non-circular gear transplanting mechanism was simplified into a plane 2R chain opening mechanism, an approximate multi-pose motion comprehensive equation was established based on the parameters of the pose points and center points, the mechanism parameters were solved through the homoethic algorithm, and rod length constraints and trajectory optimization were introduced to obtain the optimal solution (rod 1 was 100 mm, rod 2 was 240 mm). Matlab assisted optimization software was developed to complete the non-circular gear joint curve design and two-stage transmission ratio allocation, structural design was carried out by using these parameters, and virtual prototype simulation analysis was performed to verify the correctness of the sweet potato transplanting mechanism design. The physical prototype of the sweet potato transplanting mechanism was designed and field experiments were carried out. The results showed that the planting posture of the sweet potato seedlings was in line with the trajectory plan. When the planting rate was 45 plants/min, 55 plants/min and 65 plants/min, the passing rate of the planting depth, plant spacing, and under-soil horizontal length reached more than 85%. Among them, the passing rate of each item exceeded 90% at 45 plants/min, indicating the feasibility and efficiency of the mechanism, and providing a practical solution for mechanized transplanting of sweet potatoes.