To obtain the effects of curing humidity on corrosive medium transporting into concrete, a model between curing humidity and chloride diffusion coefficient was developed according to their relationships with hydration degree and porosity, which was exposed in chloride solution. An experiment was designed to verify the correct of the model, which included ordinary performance concrete and concrete mixed with fibers. All of the specimens were cured in different humidity for 28 days, and then immersed in 8% NaCl solutions for 60 and 180 days respectively. The results showed that reduction of curing humidity could increase the concentration and diffusion coefficient of chloride ions. Saturating curing can reduce the chloride diffusion coefficient by 10~20%, as dry curing increased the value about 14%~29%. This process can be slowed by mixing polypropylene and steel fibers into concrete. The material coefficients were fitted according to the test results and predicted formulas of apparent chloride diffusion coefficient were provided for the concrete after different humidity's curing.