Abstract: As for the durability of the concrete structure, the problems of steel corrosion caused by chloride ion erosion are common in the marine works. In order to accurately forecast and predict reinforcement corrosion and structure durability degradation law, the basic idea of Monte Carlo is used, combined with MATLAB toolbox to simulate the chloride ion concentration distribution around the surrounding reinforement bar. The analysis results show that in a certain period of time (10 a, 50 a, 100 a) the chloride ion concentration around reinforced bar obeys the lognormal distribution. The probability model of chloride ion diffusion is established. Judging the reinforcement corrosion by a probability method, the accuracy can be greatly increased. At the same time, the probability model is used to predict the concrete structure durability of the Lianyungang port service components, and the results are in conformity with those of the field tests. And the risk assessment is made for the failure probability of the concrete structure service life. Therefore, this model can provide a theoretical basis for the nondestructive testing of the chloride ions content in concrete and for the judgment of steel-bar corrosion in the marine concrete works.