With the method of human-computer interaction based on visualization, the optimization design of the separating-planting mechanism of rice transplanter was carried out. The mathematic model of the mechanism was established, and the optimization program with human-computer interaction based on visualization was compiled subsequently. Then, the influence of every parameter on the optimization object and restriction could be found out. Therefore, the mechanism's structural parameters, which satisfy the requirements of separating and planting seedlings, could be optimized easily through the interaction of human-computer. The results showed that this method was suitable, and it could improve the efficiency of optimization notably.