Abstract: The main factors influencing the water inrush of seam floor are studied based on geologic structure, aquifer, aquiclude and mining conditions. Eight parameters are taken as indexes for forecasting the water inrush risk, including fault intensity index, fold fractal dimension, water pressure, water abundance of "lower aquifers", water abundance of Ordovician limestone, aquiclude thickness, the percentage of mudstone and the depth of destroyed floor caused by coal mining. The paper uses analytic hierarchy process (AHP) method to sequence the main controlling factors, and then to establish the vulnerability index for evaluating water inrush risk in the floor of coal seam 10. The evaluation results show that the value of vulnerability index and water inrush risk are small in the southern part and high in the northeast of the minefield.