Taking a case of water inrush in Sangshuping coal mine, the paper discussed the grouting and water blocking technology used for the special large water inrush caused by being mined beyond the approved limits with unknown water channel. The engineering practice indicates that the situation of cross-border mining must be firstly detected to determine the general location of water interception; then the water inrush channel should be detected by geophysical methods and based on the geophysical information, the water channel position is pinpointed with downhole drilling. After dynamic water interception, the grouting is carried out in the coal seam floor and the top of Ordovician limestone.