Abstract: In order to solve the problem of the determination of the roadway roof safety distance under the dangerous goaf water, physical model of the roadway layout under the dangerous goaf water was set up. The model contains three parts from top to bottom, which are floor fracture zone, safety water-resisting zone and roadway surrounding rock loose zone. By using the theory of soil mechanics, plastoelasticity and ground pressure, the mechanism of tunnel roof water-inrush under the dangerous goaf water was analyzed and the theoretical criterion of preventing the tunnel roof water-inrush under water filling goaf was confirmed. Based on this criterion, the theoretical calculation and numerical simulation have been done to support the norm.