Stope water inrush is an accident which can cause great casualty. To study the transformation regularities of water inrush channel in the cover strata induced by the roof breakage and the roof caving, the FLUID-MECHANICAL function of the Universal Distinct Element Code (UDEC) is designed to calculate the cranny expanding and close phases during the roof breakage and recombination. Combined with the practical engineering, the features of dynamic development and dis tribution of the seepage vector, seepage velocity and its boundary are systematically analyzed. Some reasonable achievements can be applied in the prevention and cure of water inrush, which proves that the UDEC is one of the credible numerical qualitative analysis methods to forecast the cranny's initiation, propagation, close and other hazards (such as the water inrush and the groundwater runoff). The result of merical simulation shows that the water inrush channel is influenced obviously by the coal mining. The risk of water inrush is highest when the main key strata breaks, therefore this phenomenon should be paid more attention to.