To address the problems of high leaf breakage rate and poor harvesting quality in mechanical harvesting of broadleaf crops. In this paper, Yunnan Tobacco 301 and Yunnan Tobacco 121 were used as research objects to study the physical characteristics of mature leaves and the mechanical properties of stems and leaves when they were separated. Determine the physical characteristics of the plant leaves to provide a reference for the structural design of the manipulator, the clamping method and collision avoidance. In addition, a universal material testing machine was utilized to investigate the mechanical properties of the stem-leaf connection at the base of the mature leaf blade under different directional loads; and to investigate the effects of applying loads at different action points on the value of the load required for stem-leaf separation, which will provide a reference for the harvesting action of the manipulator. The results showed that: in harvesting the leaves were more likely to separate from the tobacco stalks at the stem-leaf interface, the stem-leaf interface of mature leaves was anisotropic, and the loads applied in the three directions were F1 > F2 > F3, and the value of the load required for the separation of the stalks was positively correlated with the value of the area of the main vein section; with the distance between the point of action of the loads and the interface of the stem-leaf interface increasing, the value of the load required for the separation of the stalks decreased, and the value of the load was the smallest at 50mm. This study provides a reference basis for the structural design of the manipulator and the selection of the picking method, which is conducive to the reduction of foliar damage during the picking operation.