As the global climate changes dramatically,the increasing intensity and duration of drought seriously affects plant growth and crop yield. Karst is a typical arid and high-calcium habitat,and plant leaves in karst areas contain a large amount of calcium oxalate crystals,while the relationship between the crystal and the drought tolerance of plants is not clear. In this study,we took Viola verecumda grown in karst area as material,and analyzed the relationship between the changing characteristics of calcium oxalate cyrstals and water in its leaves,by subjecting the leaves to natural dry soil. The results showed that in the early stage of drought stress,V. verecumda maintained the intracellular water balance mainly through the release of intracellular bound water. In the later stage of drought,the leaves mainly prevented water loss by closing the stoma and converting part of the free water into bound water. In addition,the density of calcium oxalate crystals had an significant positive correlation with the bound water content (r = 0.825 3,P<0.000 1),suggesting that calcium oxalate crystals act as the main matter binding water. Therefore,V. verecumda may coordinate the physiological behavior of calcium oxalate crystals and stomatal during drought tolerance.