Sandstone is different from pure brittle rocks such as marble and granite. Its brittleness weakens and then increases with increasing confining pressure. This paper establishes a calculation model of the “brittleness-ductility” energy drop coefficient that characterizes the whole process of sandstone failure from the perspective of energy. The obtained result was compared with the result of traditional calculation model. The results show that the established model is more consistent with the experimental phenomenon and can describe the whole process of sandstone failure more precisely at a macro level. Moreover, the model is more practical since it avoids the tedious integration calculation process. The model and tests have extended the applicable range and applied rock types of the energy drop coefficient and enriched the knowledge system of elastoplastic mechanics. At the same time, they carry important significance for environmental restoration and geological disaster prevention and control in sedimentary rock mining zones, which can promote the sustainable development of related industries in the mining zones.