The establishment of soil constitutive model is often grounded on the isotropic compression model. Based on the analysis of the isotropic compression characteristics of the cohesionless soils

it is found that the value of the compression index is closely related to the current void ratio and spherical stress. On this basis

an expression of the compression index formulated as a separable function of the current void ratio and spherical stress is established. Then

a three-parameter compression model that describes the compression characteristics of the cohesionless soils is obtained. The comparisons with test data of four types of sands show that the model can properly fit the relationships between void ratios and stress of cohesionless soils with different initial void ratios. Compared with the compression models established by taking the limit compression curve as the refence line

the proposed model is more useful in fitting the relationships between void ratios and stresses of cohesionless soils in low-stress regions. The model also provides a foundation for establishing constitutive models of cohesionless soil.