The mechanical properties of soil are significantly influenced by the structure: the stronger the structure is, the greater the deformation of the soil damage is, and the more significant the impact on the actual project is. At present, the special engineering properties of structural soil have been widely understood, but how to accurately describe the relationship between strength and deformation by mathematical methods is still the main research content. In this research, an experimental study is carried out on the strong structural clay distributed in Zhaotong, Yunnan. The results show that the structural yield stress is as high as 800 kPa, which is a typical strong structured soil. According to the stress-strain relationship of the conventional triaxial tests, the shear deformation of strong structural clay is divided into structural non-failure stage, structural gradual failure stage and structural complete failure stage. Based on the failure process, the traditional Duncan-Chang model is modified and the damage ratio parameter is introduced to establish a modified Duncan-Chang constitutive model suitable for strong structural clay. The initial shear modulus, the asymptotic value of the principal stress difference and the shear modulus parameters in the model are deduced and analyzed, and the parameter values are consistent with the shear deformation law of the experimental soil. Through fitting and analyzing the experimental data of existing structured soil, the results show that the modified model can better describe the stress-strain characteristics of strong structural clay.