Abstract: Tortuosity,as a macro-parameter,modifies the behavior of complicated structure of porous media in terms of mass transfer in them.So far,the clear relationship between tortuosity and the microstructure of porous media is uncertain.Because of the complexity of the porous media,accurate measurement and quantitative description are difficult by both experiment and theory.Therefore,the combination of experiment and computer simulation is necessary for discovering the inner link between tortuosity and porous media structure.In this paper a three dimensional network model based on simple cubic is used for simulating binary gas diffusion in porous media,where the pore radii obey the Rayleigh distribution and the pore length is assumed identical.The diffusion molecules are ethylene,argon,carbon dioxide and hydrogen.Firstly,the calculated tortuosity is found not change with the temperature,the kind of and the concentration of diffusion molecules for the same pore network.Then by changing the pore size distribution and mean coordination number the calculating results show that the mean coordination number is the sole factor influencing tortuosity.Meanwhile,the Wicke-Kallenbach steady state diffusion experiments are done over two types of aluminas, γ - Al 2O 3 and α -Al 2O 3,which have the different pore size distributions.The binary diffusion molecules include the three combinations of ethylene,argon and carbon dioxide,the diffusion temperature is 50—160 ℃,the experiment results confirm that tortuosity is almost the same number for each of the aluminas.Finally,from the analysis of experimental results and simulation,the tortuosity that has a close relationship with the mean coordination number can be considered as the structure parameter of porous media.