Abstract: The pore inside porous media is abstracted into a fractal curve after analysis in this paper. The fractality of the fractal curve is defined as a spectral or fracton dimension d , the value of which is in the range 1≤ d< 2 . According to a scaling relation that relates the real length of a fractal curve to its shadow and yardstick size, an equation of diffusion flux for two - component gas mixtures in porous media is deducedwhich can also be used to measure d in terms of experimental data of diffusion.After presenting a practical equation calculating the yardstick size in this case, the method to determine d is subsequently offered. The above procedure is applied to Ni /γ-Al2O3 catalyst . The result of calculation shows that the internal pores of catalyst Ni /γ-Al2O3 can be featured as a fractal with respect to gaseous diffusion processes with its spectral or fracton dimension d = 1. 10.