Abstract: Aiming at the problems of imperfect function, low automation, high rate of seedling injury, unstable plant spacing, high labor intensity and low efficiency of onion seedling transplanting in the market, in order to reduce the operation link and improve labor efficiency, this paper designs a high-efficiency and low-loss automatic transplanting machine for onion, which mainly includes the key points of seedling throwing device, seedling receiving device and seedling transplanting device.The seedling-throwing device can realize automatic intermittent whole row transportation and seedling-throwing and accurately put onion seedlings on the seedling-feeding device; the seedling-feeding device can realize orderly placement of onion seedlings on the horizontal seedling-feeding device; and the seedling-planting device can realize the high vertical transplanting of onion seedlings in different soil environments.The field transplanting test of the prototype shows that the qualified rate of planting depth is 96.9%, the seedling burying rate is 0.3%, the seedling injury rate is 0.1%, the lodging rate is 0.8%, and the pure operation productivity is 0.09 hm~2/h. The machine has good operation effect, high automation and low seedling injury rate, which meets the requirements of high efficiency and low loss. The research in this paper has certain popularization and application value for mechanized transplantation of onion.