Abstract: The whole process of acid rain corrosion to non-metal building materials was divided into three stages, namely initial stage, middle stage and last stage, and then the corresponding mechanism has been put forward. The study on the whole corrosion process shows that the damage of acid rain to the materials is a result of coordination corrosion of H⁺ and SO²₄^-; with H⁺ in acid rain, Ca(OH)₂ in hardened cement paste will dissolve and the reaction between SO²₄^- and Ca(OH₂) will produce CaSO₄·2H₂O with expanding volume. Therefore, the main cause of corrosion of non-metal building materials by acid rain is the mechanism of dissolution corrosion caused by H⁺ and expanding corrosion by SO²₄^-.