In order to investigate the primary reason of increased lodging rate due to increased operating speed of planting mechanism of rapeseed blanket seedling transplanter, the motion process of seedling transfer, seedling pushing and seedling block contacting the soil was analyzed, and the kinematics model was established. The equations of motion and force of the rapeseed blanket seedling block during the planting process and the equilibrium equations of the seedling standing were derived. The design parameters of the planting trajectory on the landing angle of seedling block, the landed angular velocity of seedling block and seedling standing situation were analyzed. Based on Matlab GUI, a blanket seedling motion process auxiliary analysis software was written to optimize a set of institutional parameters that could satisfy the requirements of rapeseed blanket seedling planting, mainly including the eccentricity of elliptical gear of 1.5, the gear module of 2.3mm, the tooth number of 19, the initial installation angle of planet carrier of 38°, the initial phase angle between the planting arm and the planet carrier of 42°, the length from the center of the planetary gear to the seedling needle tip of 142mm. Trajectory verification and bench testing were carried out. The results showed that when transplanting rapeseed blanket seedlings with seedling age of 35d and seedling height of 80mm, and setting the planting frequency of 220 holes/min, with the increase of forward speed, the lodging rate was increased and the planting qualification rate was decreased. The blanket seedling lodging rate was increased significantly when the forward speed was increased from 600mm/s to 700mm/s, which was basically consistent with the theoretical calculation of critical forward speed result of 670mm/s for seedlings standing. When the forward speed was 600mm/s, the lodging rate of the planting mechanism was 9.67%, which was 68.81% lower than before the optimization, and the qualified rate was 88.67%, which was 31.69% higher than before the optimization. Under this condition, the seedling blocks fell to the ground with upright posture, which achieved the transplanting requirements of rapeseed blanket seedlings. The correctness of the theoretical model and the reasonableness of the optimization of the trajectory parameters were verified by experiments.