In this paper, the effects of the heating temperature and holding time on the austenite grain growth of SCM435 steel were studied and analyzed in terms of the average, macro-axis and minor-axis size of the grains. The results indicated that the classical Sellars model was highly consistent for describing the growth stage of the new austenite but poorly described the initial nucleation-growth stage and stability stage of the austenite. A new model that expresses the average austenite grain growth of SCM435 steel was developed, and the values calculated based on this model were highly consistent with the actual measured values. The standard deviation and expected grain-size expressions increased as the heating temperature and holding time increased. The macro-axis and minor-axis size of the grains were linearly correlated with the average size, and the ratio of the macro-axis to the minor-axis size remained generally constant during grain growth. Furthermore, this paper provides a new way of thinking about heredity in materials science from the perspective of mathematical characteristics.