When transplanting on the film, the vegetable transplanter can only adjust the plant spacing in a small range to ensure a smaller planting hole opening, if the plant spacing is too large, it will cause the planters to move forward and tear the film, if the plant spacing is too small, it will cause the planters to move backward with the film, these will make the planting hole opening too large, and will affect the later growth of seedlings, for this reason a set of reciprocating duckbill planting device with steplessly adjustable planting static trajectory was designed. A set of planting mechanism with steplessly adjustable planting trajectory and its planting method were proposed based on the analysis of the structural characteristics of the planting device, the working process and the principle of adjusting the size parameters of the components and the installation parameters to realize the planting of smaller holes with different plant spacings. By establishing a veridical kinematic model of the mechanism, developing visual aided design software, analyzing the influence of each parameter on the planting characteristics, and using the stepwise approximation method to determine a set of parameters that met the requirements as follows：L1=35mm, L2=350mm, L3=70mm, L5=280mm, dD=358mm, Φ4=15°, xB=20mm. The position of the longitudinal coordinate yB of the pivot point B corresponding to every 50mm interval between the plants was marked. The duckbill planting device was designed and modelled in 3D according to the combination of mechanism parameters, and kinematic simulations were carried out to verify the feasibility of the duckbill planting device. Laboratory prototype tests were carried out and the results showed that the planting pass rate was greater than 90% at plant spacings between 100mm and 600mm, the coefficient of variation of plant spacing was less than 6% and the hole size was less than 100mm, with an average hole size of 52.26mm at plant spacing of 100mm.