Allowing for the analogy between ions diffusion and heat transfer, the numerical simulation on chloride ions diffusion in concrete can be realized following the thermal analysis module in the large general FEA software ANSYS, by reasonable equivalent of parameters. It is based on the modified model for Fick’s second diffusion law, taking the factors of temperature, humidity and time etc. into account. Hereby, the numerical simulation method is established for predicting the chloride concentration distribution with time in concrete, testified by the coastal exposure test. The test results confirm the efficiency and feasibility of the method.