In order to realize the high-speed work of liquid fertilizer applicator, the elliptic gear planetary galaxy as the pricking hole mechanism was designed, which presented the simple structure and steady movement. Then, the mathematical model for this mechanism was established. By Visual Basic 6.0 program, taken the distance between hole 200mm and buried depth 120～150mm as the optimization goal, the most optimum parameters range of the mechanism was obtained as follows: the initial angle between planet frame and the line formed from spraying-fertilizer needle-tip and planet wheel axle was -45°～-40°, the initial angular displacement of planet frame was 40°～50°, the distance between spraying-fertilizer needle-tip and the planetary gear axle center was 280～300mm, simultaneously, the semi-major axis of elliptic gear was 29.364mm, the teeth quantity was 23, the ratio of semi-minor axes and semi-major axis was 0.958, the radius of circular gear was 25mm. Among the optimization operational parameters, a group of parameters were selected to design the pricking hole mechanism by using Pro/E simulation. The simulation result shows that the designed pricking hole mechanism can satisfy the design requirements of the distance between holes and the buried depth.