The excavation simulation and fully-coupled model of the fractured rock in the discrete element method are used to analyze the changes in fracture aperture and the process of the flow change after excavation. The results show that the change of the fracture aperture, water pressure and fracture permeability of the fractured rock mass in the coupling conditions of the seepage and stress is a dynamic process, and also shows its interaction and interdependence. Owing to the closure of the fracture, the hydraulic gradient and the permeability pressure of the fracture turn large, and also promote the expansion of water cracks, and fissures connectivity increasing. The increase of the crack opening width will result in the increase of the infiltration capacity and seepage flow, and the reduction of seepage pressure. Because of the dynamic dependence of the fracture aperture, pressure and seepage, under certain conditions, changes in fracture aperture can lead to the formation of local water-passage, and the local emission of high pressure water, and thus promotes the formation of the sudden outgush disasters. Preliminary research shows the effectiveness of the method employed, and provides a potential research direction to study the sudden blowing in the excavation of fractured rock masses.