The working principle and structure of rice-seedling transplanter were introduced in this paper. According to the requirements of corresponding trajectory and posture of the transplanter, the transmission mechanism with non-circular gears planetary was proposed. The equations of displacement, velocity and acceleration of the mechanism were established. Also a computer-aided analytical and simulative program of the mechanism was compiled based on Visual Basic 6.0. The optimized parameters, optimized objections and main structure parameters were displayed in that software. Meanwhile, the optimized results were digitized. The influences of some important parameters on the kinematic characteristics of the mechanism were analyzed by the software. A group of preferable mechanical parameters were obtained subsequently, whose corresponding trajectory and posture could meet the demands of rice transplanting. The 3D model of the mechanism was established on the basis of the optimizing parameters, and then the virtual prototype test was done. Both of corresponding trajectory and posture met the agronomic requirements.