Abstract: To investigate the influence of lime content on loess strength and its microscopic mechanism, different proportions of lime were used to improve loess. Through direct shear test, mercury intrusion porosimetry and scanning electron microscopy, the strength characteristics and microstructure changes of compacted loess and modified loess with different lime contents were analyzed qualitatively and quantitatively, and the microscopic mechanism of lime-improved loess was analyzed in depth. The results show that the shear strength parameters of lime-improved loess increases first and then decreases with the increase of lime contents. The cohesive force and internal friction angle reach the maximum when the lime content is about 8%. The incorporation of lime gradually increases the cements between and on the surface of the skeleton particles. As the pores are filled with cements, the unstable pores gradually decrease, and the integrity is enhanced. But with too large lime content, the excess lime will accumulate between the agglomerates, which will affect the cementation. The reason for the increasing strength of lime-improved loess is that the cementing material generated by the lime hydration reaction enhances the degree of cementation between soil particles, resulting in a larger friction between the particles, a more stable soil structure, and greater soil strength. However, the excessive lime will reduce the cementation between soil particles, thus reducing the shear strength of the improved loess. The research results not only enrich the theoretical research on the strength characteristics and microstructure of loess, but also provide reference for the selection of engineering design parameters of improved loess.