In view of the threat of limestone water disaster in Taiyuan Formation of No.5 coal seam floor in East No.1 and East No.2 mining areas of Banji Coal Mine, the geological and hydrogeological conditions of the mining area were systematically analyzed. Seven main control factors covering three aspects of aquifer, aquifuge and geological structure were selected, and the evaluation system of water outburst vulnerability of coal seam floor was constructed. The constant weight was determined by the coupling of analytic hierarchy process and CRITIC method, and the variable weight evaluation model of floor water outburst was established by introducing the variable weight theory. Combined with the traditional water outburst coefficient method, the water outburst risk of limestone group I aquifer in Taiyuan group of No.5 coal floor was evaluated. The results showed that the overall water outburst risk of Taihui Group I in No.5 coal seam floor was low, and there was only local water outburst risk in the structural development areas such as faults and folds in the east wing of East No.2 mining area. The research provided a scientific basis for the prevention and control of floor water disaster in mining area.