Abstract: With respect to the defects that the water-bearing karst structure is simulated by used low -resistivity body in even high-resistivity medium, the numerical simulations of the karst structure within two layer media are made with integral equation,and the features of the calculating curves are analysed. The effects of resistivity differences among the surface layes, karst and country rock on the prospecting results are also analysed. The calculated results have practical significance for field technique and data interpretation in karst areas with electrical prospecting.