Abstract： The problem of coal seam roof water inflow（sudden water） was always a major problem in north China type coal field mining. Because the roof was located in the upper part of coal seam，coal seam mining caused stress redistribution and induced the damage of surrounding rock. When the fracture affected the roof aquifer, it might lead to sudden water of roof. Taking Boligou mine as an example, on the basis of identifying the mine hydrogeological conditions, the coal seam roof and floor water filling factors were analysed, the relatively mature "three diagram method" was adopted to evaluate coal seam roof water inflow（sudden water）. The study provided theoretical basis for underground sudden water prevention and control.
