In view of the limitation that the traditional formula of water outburst coefficient was difficult to accurately evaluate the risk of floor water outburst under the condition of high intensity mining, the formation mechanism of mining floor failure depth and Ordovician limestone top boundary lifting height was systematically studied, and an improved calculation method of water outburst coefficient was proposed. The formula of floor failure depth considering stress concentration factor was deduced, and the mechanical process of rock mass yield failure induced by mining stress was revealed. The quantitative expression of the lifting height of the Ordovician limestone micro-fracture was established, and the critical conditions of water pressure attenuation and fracture propagation termination were clarified. The mining failure zone and the confined water lifting zone were included in the theoretical framework of the ' lower three zones ', and the improved water outburst coefficient formula was constructed to make the effective aquiclude thickness more realistic. The calculation and analysis under different lithology conditions showed that the water outburst coefficient of weak rock strata including sedimentary rock increased significantly after improvement, and the risk of water outburst increased. However, the change of hard rock including magmatic rock and metamorphic rock was small, and the improved water outburst coefficient was negatively correlated with the rock strength parameters. The research results provided a more scientific theoretical basis for the risk assessment of coal mine floor water outburst under high intensity mining conditions.