Abstract: Abstract: During the operation of planting mechanism with duckbilled planting nozzle, seedlings fall into ditch or hole under the action of gravity after they are thrown into the planting nozzle, then the transplanter carries out earthing and tamp. The planting nozzle is to keep the seedling upright during the process of dropping and to make the placement accurate. The seedling is free during the entire process so it is not easy to be damaged. During the process, the friction between seedling and planting nozzle affects the drop time. Especially, with the increase of planting velocity, sometimes the seeding's movement time in planting nozzle is too long, so that seedling can't fall into ditch or hole in time, and it causes planting failure, which also has adverse effect on the next planting cycle. In order to avoid this situation, in this paper, the movement of seedling relative to planting nozzle was divided into three stages. The first stage is that seedling falls into the planting nozzle and crashes with the planting nozzle. This collision can be defined as plastic collision form the mechanical property of seedling. The second stage is that seedling does planar motion after collision. During this stage, seedling slides along the planting nozzle and spins along the collision point at the same time. The third stage is that seedling slides along the planting nozzle. During this process, the movement of seedling relative to planting nozzle can be regarded as the linear acceleration movement. This paper established differential equations for each stage. In order to verify the validity of the model, in this paper, 128-hole-plate was used, and broccoli seedling with 2-3 leaves and 63% water content was chosen as working object, and planting mechanism with planetary deformed elliptic gears was used as carrier, and analysis was conducted. Relative movement and interaction force between seedling and planting nozzle and seeding's movement time in planting nozzle were got from the analysis. The movement of seedling in planting nozzle was also studied by using high-speed camera and video processing technology. The measured time from seedling entering the planting nozzle to seedling leaving the planting nozzle basically agrees well with the calculated time. It shows that the differential equations and the calculation are correct. The analysis and experiment also show that the seedling can fall into the hole successfully, when the seedling is thrown into the planting nozzle with the angle of 55° between axis of seedling and horizontal plane, and velocity of seedling's barycenter is 1.5 m/s, and the angle between velocity direction of seedling's barycenter and horizontal plane is 68°, and the velocity of this planting mechanism is less than 147 r/min. This provides design consideration of the maximum speed for planting mechanism.