Abstract: On the basis of the theory of corrosive dynamics for RC and a lot of test data, an expression for the displacement field of the concrete around corroded steel bars is derived. By using the nonlinear finite element method based on the fictitious crack model (FCM) of fracture mechanics of concrete structure, a model is built for analyzing the whole cracking process of the corrosive cracks in RC members. Meanwhile, a computerized simulation for the corrosive cracking process of RC members is carried out with programs made by the authors. Results show that the model proposed in this paper makes it possible to acquire the critical condition for the cracking of corrosive crack and to obtain a quantitative relationship between the corrosive losing rate of steel and the width of corrosive crack.