Abstract: Hazards due to stratum separation are a type of roof water hazards that unexpectedly happen under the conditions without any water reservoir. However, the hazard origins have not been understood or explained, resulting in great difficulties in control of water hazards in coal mines. To solve the problem, Haizi Coal Mine is taken as a case study. The hydrogeological, geotechnical and mining conditions are analyzed. The roof stratum failure and displacement are analogized physically and simulated numerically. A new type of water hazards is found finally, and a new theory for the mine hazards, i.e. water hazards caused by burst of water cells formed by overburden stratum separation, is put forward. The drilling and borehole camera scanning have verified the above theory. According to the theory, the dynamic draining measures are proposed and used successfully in the control of water hazards. The research achievements are applied to other working faces with the similar hydrogeological conditions for coal mining safety. The investigation on the hazards by simulations not only theoretically fills the gap of water hazard classification for coal mines, but also finds a way for the control of water hazards in coal mines.