Abstract: A new method to evaluate leakage of karstic rock is introduced in this paper. The first step of the method is to establish a stochastic structure model of karstic rock using the data from the in situ measurement. The second step is to calculate the hydraulic conductivity tensor of karstic rock using the data from the stochastic structure model. The third step is to assess the leakage using the calculated hydraulic conductivity tensor based on the regional hydraulic condition. Then the distribution of leakage can be characterized by repeating the model runs. Among these three steps the first one is the most important and difficult step. At the end, the authors present a case study to demonstrate procedures and flow chart of the model development and its applications in engineering projects.