In order to lower the damage to the root system and pot soil of the seedling caused by the picking seedling pot mechanism in the tomato pot seedling transplanting process, and avoid the optimization problem of special seedling-picking trajectory and posture design of the mechanical pot seedling transplanting mechanism, the extensible type of picking seedling pot mechanism that can be used in conjunction with a series of transplanting mechanisms was proposed. It was achievable that the seedling needles of the mechanism at key positions of the picking seedling completed the process of protruding into the seedling pot, moving and delivering seedlings, and retrieving and pushing seedlings at a fixed angle. Based on the analysis and design requirements of the process of transplanting and picking seedling pot, the mechanical analysis model of the picking seedling pot mechanism was established, and the factors affecting the minimum driving force on the driving rod when the seedling needles protruding into the seedling pot were obtained. A computer-aided analysis and design software for the picking seedling pot mechanism was developed based on the Matlab App Designer platform, obtaining a set of picking seedling pot mechanism design parameters that met the requirements of tomato pot seedling transplantation. Using the three-factor five-level quadratic regression orthogonal rotation center combination test method, taking the angle of inclined rods, moisture content of seedling pot and depth into the pot as the test factors, and taking the integrity rate of the pot and the success rate of taking seedlings as the evaluation indexes, the prototype was trial manufactured and the bench was built to implement the parameter combination optimization and verification test. The results showed that the extensible type of picking seedling pot mechanism could effectively cooperate with the seedling picking mechanism to complete the performance requirements. The results showed that the operation effect was the best when the combination parameters included angle of the driving inclined rods was 112°, the moisture content of the seedling pot was 57.5%, and the depth into the pot was 28.4mm. The integrity rate of the seedling pot was 96.44%, and the success rate of picking seedlings was 97.06%, which met the performance of pot seedling transplanting.