Aiming at the problems of seedlings injury, seedling pot cracking and high matrix loss rate in the operation process of automatic seedling device, a eject lifting type device for pot seedling detaching from movable tray was designed. The device was mainly composed of seedling tray conveyor, tray positioning mechanism, opening and lifting mechanism and control system. According to the structure of the movable tray, a three-dimensional positioning mechanism composed of half Y shaped positioning bars, guidance positioning wheels and positioning plates was designed to position the tray from longitudinal, transverse and vertical directions, so as to ensure that movable tray could be accurately positioned in operating area. According to the characteristics that the pot hole of movable tray could be opened, an opening and lifting mechanism consisting of short push plate, long push plate and lifting platform was designed. Short push plate and long push plate were sequentially opened by longitudinal side plate and lateral side plate which were used for movable tray positioning so as to separate seedling pot from pot hole. At the same time, after the separation, lifting platform lifted seedling pot which started to slide along the wall of pot hole from bottom and lifted it to the designed height for subsequent operations. The control system of device for seedling detaching from movable tray was designed. PLC controlled the operation of each driving motor according to the outputs signals of the movement sequence of each mechanism, so that each mechanism could coordinate in order to realize the automatic detaching of seedling pot from movable tray. In order to verify the operation effects of the device for seedling detaching from movable tray, bench experiments were carried out. Seedling pot lifting speed, type of the end face of lifting platform and moisture content of matrix of seedling pot were used as experimental factors. The qualified rate of position of seedling pot on the end face of the lifting platform and the loss rate of seedling pot matrix in process of seedling pot detaching from movable tray were taken as the evaluation indexes. Rapeseed seedlings of 35-day-old which were cultured in a 16-hole movable tray were used as the object. An experimental scheme of L9 (34) orthogonal table was used for the bench experiments to study the influence of various factors on the evaluation indexes. Through the range analysis and variance analysis of experimental data, the influence order of each factor on the evaluation indexes were obtained, which were material type of end face of lifting platform, seedling pot lifting speed and moisture content of matrix of seedling pot. At the same time, the optimal parameter combination of the experimental factors was obtained in the experiments: the lifting speed was 32 mm/s, the material of the end face of lifting platform was rubber, and the moisture content of the matrix was 55%. Verification experiments with optimal parameter combination were carried out and the results showed the qualified rate of positions of seedling pot on the end face of the lifting platform was 100% and the loss rate of seedling pot matrix was 1.56%, which indicated that the device for seedling pot detaching from movable tray met the requirement of actual operations. The study provides important theoretical basis and reference for the design and further study on seeding automatic pick-up and transplanting mechanism.