Abstract: Coal mine water hazard is one of the five major natural disasters in mines. Damage by water in separated stratum has been a frequent and harmful form of water damage in recent years. During the process of water inrush from separated stratum，the water of aquifer enters the separation space first，and then enters the mine due to the rupture of the waterproof layers below the separation space. Therefore，the calculation of the amount of stratifugic water is of great significance to the prediction of the amount of water inrush from separated stratum and the possibility of water inrush. Three water inrushes from separated stratum occurred in the 1304 working face of Jinyuan Zhaoxian Coal Mine，Shaanxi Province. This paper analyzes and summarizes the variation law of water level and water volume in the process of water inrush from separated stratum，establishes the hydrogeological model of stratifugic water，the prediction method of water volume and calculates it. Then it divides the amount of water inrush from separated stratum，compares the divided water volume with the estimated water volume，studies the relationship between the amount of water accumulated and the separation space，especially the separation height，and validates the forecasting effect of the amount of water accumulated and separation height on water inrush.Through the above work，it is concluded that:① The abnormal drop of groundwater level can be used as a warning basis for the water inrush from separated stratum. For example，before the first water inrush from separated stratum at the 1304 working face of Zhaoxian Coal Mine，the water level of long hydrological observation hole began to decline six days in advance，with a cumulative drop of 23.39 m and an average decline rate of 4.253 m/d. ② Based on the semi infinite confluent model of an aquifer，the estimation method of the amount of stratifugic water is reliable. In the three cases of water inrush in the Zhaoxian Coal Mine，the error between the estimation method of groundwater dynamics and the method of segmenting the water quantity is 0.20%-8.35%. ③ According to the drop of groundwater level，the critical values of separation space and separation height can be calculated. The separation heights of the three water inrushes in the Zhaoxian Mine are 0.75，1.08 and 0.87 m，and the critical value can be used to further predict the possibility of water inrush from separated stratum.The critical value of separation height proposed in this paper needs to be further studied based on mechanical theory and summed up from a large number of water inrush cases in the future.