Abstract:The theory of environmental isotope and hydrochemistry applied to leakage study is described. As natural tracers,environmental isotope and hydrochemistry mark groundwater,river water and precipitation. By contrast of the composition of environment isotope and water chemistry in water,the relation between them can be determined to distinguish the replenishment resource of groundwater,the position and range of leakage,the stratum formation and and so on. Some conclusions are drawn and also proved by other methods in three examples. So it can be concluded that environmental isotope and hydrochemistry can be used as a useful measure for dike leakage study and a guidance for dike reinforcement.