In order to set up the dynamics model of the transplanting mechanism with planetary elliptic gears of high-speed rice transplanter, the effect of seedling-pushing device on it must be analyzed. In this paper, the dynamics characteristics of seedling-pushing device were analyzed by method which was derived by authors. The method is analytical form differential equations of rigid body compound motion. As a result, the dynamics model of seedling-pushing device was deduced. By programming calculation. Some conclusions were drawn: ①the relationship between the angle of gears trunk and the angle of shifter and the position of seedling-pushing rod in the course of seedling-pushing and collision, which were tested and verified by high-speed Video Tape Recorder; ②the relationship between the angle of gears trunk and the bearing force of spring, shifter shaft and seedling-pushing rod in the course of seedling-pushing and collision. These conclusions provide basis to analyze this kind of transplanting mechanism.