Building materials have requirements of high-strength and low-density, and it is necessary to establish evaluation indexes that are suitable for optimizing the mechanical properties of building materials. Under the background of density and strength evaluation, a method for comprehensive evaluation of the density and strength of building materials, density-strength method, is proposed. Based on the density-strength method, the optimization of different materials and the optimization of different parameters of the same material are carried out, and the distribution of the density and strength parameters of different building materials in the density-strength diagram is studied. The results show that the density and strength of different materials is different on the density-strength diagram, and when selecting materials, the density-strength diagram can be used to calculate the relative density improvement amount and the improvement angle of each material for comparison and selection; the density and strength of the same material under different parameters are different, and the factors affecting the properties of the material can be optimized by the density-strength diagram; density and strength can comprehensively reflect the properties of density and strength of building materials, which is an intuitive and understandable method to express the lightweight and high strength of materials.