Abstract: The stress partitioning constitutive framework for methane hydrate-bearing sediments (SPF-MHBS) assumes that the skeleton matrix and hydrates share the effective stress on the MHBS while deforming under the same strain, allowing independent establishment of constitutive relations for the two components. Based on this concept, the effective stress transfer between the hydrate and the skeleton matrix during loading and hydrate dissociation is naturally captured under both constant and changing hydrate saturation conditions. This study constructs a constitutive model based on SPF-MHBS, which can describe the mechanical properties of MHBS during hydrate decomposition. The clay and sand unified hardening (CSUH) model is applied to the skeleton, by introducing the "equivalent void ratio" considering the influence of hydrates on the compactness and dilation characteristics of the skeleton. An isotropic elastic damage model is adopted for hydrate, which can reflect the strength variations of hydrate during loading/unloading, dissociation, and temperature/pressure changes. Compared with the laboratory test results, it is verified that the model can uniformly describe the stress-strain relationships of both silty and sandy hydrate-bearing sediments under various isotropic compression, drained shear, and dissociation conditions.