Existing rotary planting mechanism perform is not well in planting large spacing vegetable pot-seedling (plants spacing above 450mm) in the practical transplanting work. A new planting mechanism with planetary gear train, which is suitable for planting pot-seedling with large plants spacing, was designed. By constructing a transmission ratio function of the non-circular gears and calculating the center coordinates of each parts, the kinematic model of the planting mechanism was established, including the equations of (angular) displacement, (angular) velocity for the end point of planting mouth. According to the established mathematical model, computeraided analysis and optimization software of the mechanism based on Visual Basic 6.0 was developed. Then through analyzing the planting trajectory, which was influenced by several key parameters including center distance of the non-circular gears, angular displacement coefficients, initial installation angle of the planetary carrier, the planting mouth and the middle non-circular gear, etc., and also using the human-computer conversation optimization method，a set of mechanism parameters were found to meet the requirements of vegetable pot-seedling planting．Based on the optimized parameters, 3D model was established and simulation analysis was proceeded. Then, physical prototype of the planting mechanism was made and field planting experiments were conducted. Land planting tests were carried out and the different opening and closing time of the planting mouth impacting on the upright degree and success rate of the planted vegetables potseedling were researched. It is proved that the best opening time is when the planting mouth arrives at 10mm distance above its lowest position, in this case, the rate of seedling perpendicularity reaches 85%, planting efficiency is 100 plants/(min· row) and plants spacing is 450mm. Thus the mechanism was verified suitable for large spacing planting of vegetable pot-seedling.