Abstract: The approximate function was led to mathematical modeling in material corrosion. By the characteristic of corrosion data, the divisional mathematical modeling concept was proposed. And it was compared with three models, which were gray model, dynamic data & bi-directional difference model and power function model respectively. The results told us that approximate function model owned not only strong adaptation but applied foreground in engineering as well, besides the highest accuracy over the other three models. From the models posed in this article, we suggested that 'critical point in material corrosion' should exist to some extent.