Abstract: Soil structure is the main reason causing the differences between natural and remolded soils. The soil structure have impacts on methods and means of geotechnical engineering. This paper establishes a structural constitutive model of Haikou red clay. Based on structural quantitative indicators, the concept of comprehensive structure potential is introduced. It builds quantitative expression among geotechnical microstructure, cementation and macroscopic mechanical effects. The stress typical structural parameter and strain typical structural parameter are defined. They are obtained through the isotropic consolidation test and p=constant shearing test respectively. Both parameters exist the normalized linearization relationship relative to average principal stress. The result can describe the Haikou undisturbed red clay structure. These parameters are used to modify the K-G model. A numerical simulation is carried out. Results showed that the modified K-G model can describe the structure of Haikou undisturbed red clay, and well predict the stress-strain relationship of undisturbed red soil.