An average modified coefficient was used to modify Fick's second law and a theoretical equation was established to describe unsteady state gas diffusion in fractal porous media.The experimental system for unsteady state gas diffusion in fractal porous media was based on the plug flow diffusion.Three different porous medium samples were used to verify and modify the theoretical equation.The results indicate that Fick's second law is not applicable to unsteady state diffusion in fractal porous media

and unsteady state diffusion law in porous media is same under different conditions

and diffusion law in porous media with different pore structures is different.