The liquidus temperature of steel is greatly affected by its chemical composition; therefore, the value of the liquidus temperature can vary among different types of steel. In this study, on the basis of the concept of differentiation, the Fe-i binary phase diagram is analyzed using Photoshop image processing software. The effects of eleven common alloying elements (C, Si, Mn, P, S, Ca, Ni, Cu, Cr, Nb, and Mo, whose content is between 0%～4%) on the melting point of pure iron are analyzed. This analysis proves the following assumption to be incorrect: the relationship between the change in liquidus temperature and the content of element i is a linear relationship; this assumption is the basis of traditional liquidus calculation models. A new model for calculating the liquidus temperature of steel is established in this study. As compared to data from other literature, the model proposed in this paper has good generality and the calculation error of the liquidus temperature of steel is between ?3 and 4 °C, which is acceptable. A statistical analysis of the experimental data for different steel grades (obtained from Laiwu Special Steel) using the developed model showed that 87.2% of the absolute deviation values of the temperature are within 4°C. This result shows the model to be both reasonable and credible.