Abstract: The relationship between the strength and the density of cemented soil is analyzed from microstructure with regard to the deficiency and limitation of the researches on the density of cemented soil, which has an important impact on it. At first a basic model for the cemented soil is proposed from the basic characteristics of its microstructure, and an equation for the relation between the unconfined compressive strength and the density of cemented soil is derived. Through the basic experimental data, the basic parameters and the relevant equation are proposed. Then other basic experimental data are used to validate the accuracy of the proposed equation. The results show that the basic experimental data and the simulated values are approximately equal, hence the proposed equation is proved to be right. At the same time the microstructural model for the cemented soil is correct to some extent.