Grain boundary model in phase-field simulation during microstructure evolution in solid states is discussed based on the way to express grain boundary and its physical background. The effects of different values of simulation parameters on feature of grain boundary in the phase field model are investigated systematically and a new conception of grain boundary range is suggested based on the simulation results of recrystallization of AZ31 magnesium alloy. The gradient range of the order parameter expresses the boundary range, whose physical meaning is found to be the range of grain boundary energy distribution across the boundary. The range is also corresponding to the segregation range of alloying elements around the boundary. It is shown that the gradient parameter determines the boundary range but the grain boundary energy is determined by both the gradient parameter and the coupling parameter. The effect of the boundary range value on microstructure feature is examined by simulating the recrystallization of the alloy. The simulation results are consistent well with reported experimental measurements when the boundary range has a value of 1.18 μm. Grain growth phase-field simulation in industrial space and time scale is realized for the first time using the new model developed by introducing the new conception of the grain boundary range.