The plant factory rock wool block seedling transplantation equipment has a low penetration rate at present, and most of the operation still relies on manual labor, which is labor-intensive and inefficient. A high-speed transplantation mechanism combining secondary variable spacing for hydroponic leafy vegetable seedlings in plant factories was designed, and it was also equipped with a finger-type planting cup separation mechanism. The stress analysis of rock wool block seedlings in the process of transplanting hand picking seedlings was carried out to provide basis for the design of transplanting hand. The drop cup test of the finger-type planting cup separation mechanism was carried out to lay the foundation for the subsequent planting of seedlings to the planting cup of the cultivation slot. The transplanting mechanism test bench was built, and the transplanting success rate was tested by five-factor three-level orthogonal test with the grasping seedling depth, water content of rock wool block, overall traverse speed, lifting speed, and clamping spacing as the test factors. The influence of each factor on the success rate index was analyzed by variance analysis. The test showed that the seedling depth was 24mm, rock wool block water content was 90%, overall traverse speed was 0.8m/s, lifting speed was 0.24m/s, clamping spacing was 14mm, the transplantation success rate of the mechanism was 97.9%, and the transplant speed reached 3.132 plants/h. which can meet the technical requirements of high-speed, high-efficiency and stable mechanized operation of rock wool block leaf vegetable seedling transplanting in plant factory.