In the process of hydroponic leafy vegetable cultivation, plug seeding needs to be sparsely planted into the cultivation trough. Traditional manual operation has high labor intensity and low efficiency, which limits large-scale production. A double row end effectors with variable spacing sparse transplanting device for pot seedling in greenhouse was designed, which realized double row automatic seedling picking in the tray and variable spacing planting in the cultivation trough. A seedling picking and end effector with secondary clamping function was designed. The rigid-flexible coupling simulation test was analyzed by ADAMS and ANSYS software, and the optimum seedling depth was got as 48mm. According to the analysis of sparse transplanting operation conditions, three sparse picking seedling strategies for double row transplanter were proposed. And the optimal seedling transplanting motion strategy with the smallest longitudinal displacement of double row（row 1st and row 7th）was selected. and it was compared with the other two motion strategies. The action sequence optimization analysis of spare planting transplanting was carried out, and the time point of overlapping action sequence was optimized. The comparative experiment of 12 kinds of operation about work time sequence optimization transplanting was further carried out. The experimental results showed that the combination was the best when moving and lateral variable spacing expansion, longitudinal variable spacing separation and the descending sequence were parallel. The average efficiency of transplanting was 4836 plants/h, and the success rate of transplanting was 95.8%.