To effectively reduce the damage to seedling stem caused by transplanting mechanism in the process of picking seedling，for the seedling pickup device penetrating into the root mass，an innovative extensible potted tomatoes seedling transplanting mechanism was proposed. Kinematic theory model was established according to its characteristic and working principle，computeraided analysis and optimization software was developed and used to obtain a set of structure parameters that satisfied the potted tomatoes seedling transplanting requirements. Absolute angle of the transplantingarm and absolute trajectory was analyzed，and the rationality and feasibility of the structural parameters were verified. The threedimensional modeling of the transplanting mechanism was established, which was used for the simulation testing，a physical prototype of the transplanting mechanism was subjected to the test bench on which the highspeed photography experiments were conducted，the results of working trajectory， theoretical trajectory and the virtual trajectory were essentially identical，verifying the validity and feasibility of the design. The performance test showed that the seedling picking was satisfactory as 92.8%，the transplanting success rate was 89.7％，the acceptability of planting was 86.4％ and the planting excellent rate was 59.4％，the quality of transplanting was satisfactory. The transplanting mechanism can meet the technical requirements of tomato pot seedlings transplanting，which would provide references for the design and development of the tomato transplanting mechanism.