The physiological role of plant, such as photosynthesis, is affected by water status. Water status of the plant can be reflected by leaf tensity. Foliar water potential and physiological capacitance has a coupling relationship with the cell sap concentration. Foliar physiological capacitance is associated with the effective thickness and area of leaf. The ratio of the area of leaf and effective thickness was defined as leaf tensity. According to this coupling relationship, the relational model of leaf tensity and water potential, physiological capacitance was derived. Leaves of Broussonetia papyrifera and Mulberry alba which grow in nature were selected as experiment materials. Physiological capacitance and water potential at different time were determined. Leaf tensity at different time was calculated by using the relational model. The result showed that there were differences between leaf tensity of Broussonetia papyrifera and Mulberry alba at different determination time. The correlation coefficient between photosynthetic parameters and leaf tensity of Broussonetia papyrifera was 0.933, physiological capacitance was 0.926 and water potential was 0.631, respectively. The correlation coefficient between photosynthetic indexes and leaf tensity of Mulberry alba was 0.843, physiological capacitance was 0.820 and water potential was 0.217, respectively. It demonstrated that the leaf tensity could better reflect the changes in water status of plant than physiological capacitance or water potential.