Abstract: The fracture-cavity carbonate reservoir is developed with fractures and cavity in large scale and strongly heterogeneous. The fractures and cavity of large scale play a dominant role in reservoir fluid flow. Therefore, the multimedium models based on continuum theory are not suitable for the description of fluid flow. According to the geological features of the large-scale distribution of fracture and cavity, this paper presents a composite architecture of discretefracture-cavity model to describe the fluid flow in the reservoir. This model describes the fractures with plates, the cavity with irregular polyhedrons of large permeability and high porosity. Then, the fracture faces are discretized with triangle elements of two dimensions, and the cavity and matrix are discretized with tetrahedron of three dimensions. The seepage model of discrete-fracture-cavity is solved by mixed finite element method. The wellbore pressure response curve and pressure fields in three dimensions are obtained. The analysis of log-log type curve of wellbore pressure and pressure fields shows that six flow regimes may appear in the model. The e ects of the di erent parameters to log-log type curve are analyzed. A filed data example is analyzed by the present model.