Abstract: Acid red 12^#, a long chain multi-benzene ring coloring dye, was used as the representative compound to decide the adsorption isotherm formula of it in a mesoporous material and the relationship between the equilibrium closing rate and time by effective diffusion coefficient testing. Based on the theory of similar rate equations between unsteady diffusion mass transfer and heat conduction, the effective diffusion coefficient of acid red 12^# in the mesoporous material was solved and simulated by using the Peterson heat conduction approximate formula and transcendental equation resolved by computer, which is helpful to study the adsorption mechanism of mesoporous materials.