Abstract: The effective evaluation on the roof water inrush risk is the basic prerequisite and important basis for coal mine water hazard control and safe coal mining. In this paper, the state variables and primary and secondary control variables were determined by studying the floor water inrush catastrophe mechanism, based on the cusp catastrophe model, the equilibrium surface equation was established, and the equation expressions in the new coordinates were obtained by the conversion of the coordinates (the coordinate of state variables and the coordinate of primary and secondary control variables). The equation group was constructed with the new coordinates and used to solve the coefficient of the equilibrium surface quation and the origin position of the new coordinates, and the rationality of the result was verified by using the known water inrush point information. Based on the root criterion in the new coordinates, the water inrush risk assessment model was established, with this model, the evaluation was carried on the floor water inrush risk of No.2₁ coal seam in Xinan Mine, and the fitting rate of the model was 100%, which proved that the evaluation results were true and relibale.