Abstract: The safety and stability of submarine anchoring system of marine platforms are dependent on the engineering properties of marine sediment. The consolidation tests and triaxial drainage shear tests are carried out on undisturbed and remolded deep-sea sediment in the western basin of South China Sea obtained by the Jiageng shared voyage in 2020. The effects of structure on the mechanical and deformation characteristics of undisturbed deep-sea sediment are discussed. By analyzing the sedimentary environment of marine sediment and the formation process of inter-particle cementation, the effective stress is modified, and the degree of structure is newly defined. The normal compression index is assumed to be a function of the degree of structure. By introducing an evolution law for the degree of structure, an elastoplastic constitutive model considering the inter-particle cementation of undisturbed marine sediment is established based on the modified Cam-clay model. The effectiveness of the constitutive model is verified by comparing the predicted results with the experimental ones. The results show that the compression curve of undisturbed deep-sea sediment is highly nonlinear, and its compressibility increases rapidly with the increase of loads, and the compression curve of undisturbed deep-sea sediment gradually approaches that of the remolded sediment. Under the same confining pressure, the shear strength of the undisturbed sediment is lower than that of the remolded sediment, while the volume change of the undisturbed sediment is greater than that of the remolded sediment. By comparing the consolidation and triaxial shear test results with the predicted results, it is found that the proposed model can describe the stress-strain characteristics of undisturbed marine sediment well under different stress states. The research results will provide a theoretical basis for the stability analysis of submarine anchorage system and the prevention and control of submarine engineering disasters.