At present, most of the work that taking trays out from the rice nursery seedling planter is completed one by one manually, which is laborintensive and inefficient. There are some tray stackers can realize the function of automatic stacking, but the existing devices are only suitable for hard trays. Aiming at above problems, the automatic tray stacking device of rice precision seeding for nursing seedlings pipeline, suitable for both hard and soft trays, was developed to improve productivity and reduce labor intensity. According to the characteristics of common hard tray, the pallet of soft tray was developed for stacking. Besides, the transportation mechanism was designed through analyzing the conveying model. Based on the programmable logic controller（PLC）, the trays were detected by a proximity switch of the control system, and the tray stacking mechanism was controlled to lift and drop the trays to achieved the tray stacking automatically（2~4 trays per stack is available）. In addition, the cover plate of the soil antifalling mechanism was controlled to lift after stacking and finally the device can effectively prevent the soil falling out of the tray in the process of stacking that lead to seeds exposed. For detecting the performance of automatic tray stacking device, the orthogonal experiment was carried out which regarded stacking success rate and seeds exposed rate as indexes and regarded the lifting speed of tray stacking mechanism, cover plate installation conditions and productivity as factors. Orthogonal experiment results showed that the lifting speed had more influence on success rate while the lifting speed and cover plate installation conditions had more influence on seeds exposed rate. When the lifting speed was 0.15m/s, the cover plate installing with pneumatic cylinder and the productivity was 600~800 trays per hour, the stacking success rate of hard tray and soft tray was 100% and 99%~100% respectively while the seeds exposed rate was 0.28% and 0.60% respectively. The automatic tray stacking device can effectively raise productivity and reduce labor intensity, and the experimental indexes meet the using requirements of rice precision seedling.