Abstract: In order to overcome the shortcomings of AHP subjective right, at the same time to avoid the error of entropy objective affirmation inconsistent with the actual importance degree of the major controlling factors, the risk assessment of water inrush from Ordovician limestone floor of seam No.3 in Sanyuan mine, Changzhi was taken as example, the entropy weight and the analytic hierarchy process were coupled to determine the weight of the major controlling factors of water inrush from seam floor and to set up the vulnerability index model, K mean clustering method was used to conduct cluster partition of the vulnerability index value, three threshold values were determined. According to the degree of water inrush danger, the study area was divided into 4 zones:safe zone, the relatively safe zone, the transitional zone and the dangerous zone. Comparative verification proved that the evaluation results were consistent with the actual situation.