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Diffusion coefficient is one of the parameters which can describe the rate of chloride ion diffusion in concrete. This can be obtained by the chloride ion profile. By determining this factor,one can predict when the chloride ion concentration on the reinforcement surface reaches a critical value,and the cover tickness which is needed for preventing corrosion. Time and distance dependency of chloride ion diffusion coefficient has been proved by researchers,but the exact equation of dependency is ambiguous. In this paper,Researchers try to collect the various opinions about the quality of chloride ion diffusion time-dependency and then compare the experimental approaches with a new analytical approach to calculate diffusion decay index.