Mechanical properties of plug seedlings related to auto-transplanting were analyzed by tests of clamping seedling to pull it out, friction tests of the plug seedling bowl and the plane compression tests of the bowl, which provided the basis for mechanism design. Technical design of the auto-picking seedling was carried out in order to acquire the theoretical relationship between pulling force, compressive strength of the bowl, gripping angle, gripping size and friction coefficient for the picking seedling end-effector of two-needle gripping type. The picking seedling end-effector adapting to mechanical properties of plug seedlings was designed according to the mechanical characteristics of plug seedling by using gripping parameters relationship. Gripping forces were studied by the physical prototype testing. Test results showed that there was no significant difference between gripping force testing data and calculated data, which demonstrated the reliability of the theoretical design. When the frequency of picking seedlings was 30 plants per minute, the success rate of picking seelings in the testing moisture contents was up to 95.16%.