Based on the theory of chloride diffusion and pore fractal theory a new model is proposed on the base that the sinuosity of chloride diffusion characterized by the axis fractal dimension of the small pore and the porosity of concrete modified by the surface fractal dimension of large pore. The model was applied to analyze 14 d and 28 d age concrete with different proportions and the results, showed a linear relationship with those of he Coulomb electric charge determined by The Rapid Chloride Permeability Test (RCPT)—American Society of Testing and Materials (ASTM) test method C1202. The Chloride diffusion coefficient modified by pore fractal theory was presented in this study. Two different chloride concentrations in different depths of concrete were calculated by modified Chloride diffusion coefficient and orthodox Chloride diffusion coefficient. The comparison between two different Chloride diffusion coefficient indicated that the chloride concentration calculated by modified Chloride diffusion coefficient agreed better with the measured chloride concentration.