Abstract: An approach for the analysis of three dimensional ground water transient flow in a fractured rock mass is presented. Flow in the dominant fracture system is described by a distinct medium model, while flow in the network fracture system is described by a continuous medium model, and the two models are coupled together by hydraulic head and flux.It is assumed that the continuous medium occupies the entire studied domain, and the distinct medium is embedded into the continuous medium according to the spatial distribution of the dominant fractures. The coupled model calculated one-by-one the fluid flow in the dominant fractures which are functioned as the major water transport conduits, and it avoids unnecessary calculating fluid flow in individual network fractures which are numerous in number. In this way, the method can be applied to a large-sized calculation domain.Theoretical calibration results show that the coupled model can better reveal the flow properties of ground water in a fractured rock mass. Case study of the model in Wujiang Goupitan hydropower project for the calibration of ground water flow in the carbonate rock mass indicates that the method presented is practical and effective.