To satisfy the requirements of high working efficiency and smooth operation of liquid-fertilizer applicator, a kind of transmission mechanism with planetary elliptic gears was designed for deep-fertilization of liquid fertilizer. The analysis model of this mechanism was established. Its kinematic model was accomplished by means of theoretical derivation. Optimization design on the flow route of liquid fertilizer was conducted by employing the method of anti-twisting design of the mechanism. Finally, the mechanism was tested on the test-bed. After the data processing by using Design-Expert 6.0.1 software, the optimum working parameters were determined, which the working pressure of liquid pump is 0.47 MPa, the rotating rate of planetary frame is 40 r/min, therefore, the fertilizer volume is 20 mL at a time, and fertilizer loss rate is 3.2%. Observation from the test showed that, the mechanism ran smoothly with no interference, the liquid fertilizer transmitted smoothly characterized by reliable seal, which met the requirement of the design. 