Abstract: The chemical reactions between fluid and porous matrix affect greatly the mass transfer process in porous media. A convection-reaction-diffusion mathematical model is thus developed by deriving a comprehensive formula of the representative elementary volume (REV), to describe the mass transfer process in porous media when the fluid and porous matrix take reversible chemical reaction. A numerical solution to the model is available by way of the finite volume implicit method. Taking the indirect reduction of iron ore in static bed into account, the influences of such main parameters as flow rate, particle size, equilibrium constant in chemical reaction and reaction rate and the ratio of the Peclet number to the Thiele number on the distribution of gas concentration and of fractional solid conversion are all analyzed. The results are useful for the conceptual design and operation of reactor.