Abstract: When the water cooled metallic mold is used to produce the centrifugal casting of ductile iron pipe, the cementite always forms in the cast structure. It will negatively influence the mechanical properties of pipe. And therefore the cast pipe must be treated by means of high temperature annealing. In this article, according to the theory of diffusion of elements, the mathematic model of relationship between cast structure of ductile iron pipe and the annealing time of high temperature heat treatment has been built up, and the analytical formula has been introduced. The crrectivity of this formula was proved by experimental data. This formula can be used in centrifugal pipe production to increase the production efficiency and save the energy.