As the existing rice pot seedling transplanter with fixed rowspacing failed to meet the agronomic requirements of rice transplanting with different rowspaces in the double cropping rice area in south China，a kind of pot seedling transplanting device gearing to the need of variable rowspacing transplanting was accordingly designed based on the existing walking type rice transplanter. Firstly，the optimal pulling angle of pot seedlings and the location of picking and falling determined the trajectory of pot seedlings，and the kinematics model of connecting rod mechanism of picking seedlings was established， the design of the mechanism model was optimized with the help of Matlab. Secondly，according to the motion parameters of the connecting rod mechanism and the motion requirements of the clamping motion posed by the dropping posture of the pot seedling when it was being thrown，the CAM of the clamping motion control was designed，and the motion simulation was carried out to analyze the synchronism of the movement between the connecting rod mechanism and the clamping motion. Then，in order to maintain the consistency of the time when the pot seedlings fell into the paddy field after passing through the transmission tube to ensure the uniform plant spacing during transplanting，the wall inclination angle of the key parameters of the transmission tube was theoretically analyzed and designed. Finally，transplanting experiments were carried out with different seedling speeds and rowspacings，and the average successful rate of seedling extraction reached 89.96% and the average inverted seedling rate was 3.45%，indicating that the device had a good transplanting effect and could be applied to the transplanting of rice pot seedlings with variable row-spacing.