Abstract: Method for determining, from a 3D image, the values of hydraulic parameters such as the large-scale equivalent permeability, the permeability of blocks and the matrix-fracture exchange coefficient .alpha. of a fractured porous medium such as a geologic formation. The method mainly comprises discretization of the medium by means of a grid pattern and fast and approximate solution, in this grid pattern, of equations modelling diffusion of the fluids in the medium, determination of the variation with time of a large-scale transfer function (f(t), f(s)) characterizing the fluid flows from the matrix to the fractures, by simulation of the movement of particles performing random walks in continuous time on said grid pattern and suitable processing of a state function (.epsilon.(.tau.)) indicative of the presence thereof either in the matrix or in a fracture. The method can be applied for large-scale modelling of fractured oil reservoirs allowing well test interpretation.