Probability analysis on the durable life of concrete structure under chloride environment is little known. Using the probability method based on the second Fick’s law, research work was carried out to investigate the distribution factors that may influence the durable life of concrete structures. Due to the deficiency of decisive method to predict durable life, A method——based on the regulated reliability index is proposed. The relationship between durable reliability index and the corrosion time is established. The paper takes the time when the durable reliability index falls below the stipulated index as the end of durable life. The proposed method of durable life about concrete structure under chloride erosion environment is improved.