Abstract: A cusp catastrophic model of water-inrush from coal floor is established and a mechanism for water inrush due to the floor instability and destruction is analysed in the paper. The ratio of water pressure and stress, I p, can be derived from the model. When I p1,water-inrush from the floor can be caused. When I p1, water-inrush from coal floor can not be caused. The critical depth of the mining water-conducting fissure zone, h 1l, for water inrush from coal floor can be derived from the bifurcation curve equation. When h 1h 1l, water inrush from coal floor can be caused. When h 1h 1l, water-inrush from coal floor can not be caused.