Abstract: This paper gives the free energy expression of grain evolution during heating of materials on the basis of the interaction between double-well potential function and field variable.The diffusion phase field model for describing the grain growth has been established and the relevant numerical simulation software has also been compiled.The numerical simulations of normal and abnormal grain growth have been conducted based on the numerical simulation software during heating of steel AerMet100.The simulated results show that the evolution tendency of grain growth depends on the tropism number of orientation field variable.The abnormal grain growth occurs with decreasing the tropism number.