A seedling pickup mechanism which was driven by planetary secondorder elliptic gear system was developed. The work principle and structural features of the seedling pickup mechanism were introduced. The kinematics model was established, the kinematics property was analyzed and the kinematics simulation was carried out．Both the trajectory and pose of the seedling pickup claw were all analyzed. According to vegetable transplanting agronomy, the best way of separating the seedlings from plug was discussed. Based on the analysis and the simulation mentioned above，structural parameters of the planetary secondorder elliptic gear system were optimized, such as eccentricity ratio of the elliptic gear, the angle between the first middle gear and the second middle gear, the initial angle of planetary carrier and the initial installation angle of pickup claw in respect to it. The optimized seedlings pickup mechanism could take seedlings out of plug along a linear path and release it with upright posture. Finally, an experiment bench with rotary pickingup mechanism was developed and produced. Experiments were carried out to validate the optimization. The result of experiments showed that, at the working frequency of 80 plants per minute, the average success rate of pickingup seedling was 91.3%. 