Abstract: The simulation of soil constitutive properties of methane hydrate-bearing sediments is very important for the safe exploitation of methane hydrates. First, the influence mechanism of hydrate on the mechanical properties of sediments such as strength, dilatancy and softening is analyzed. The higher hydrate saturation has a significant effect on mechanical properties of methane hydrate bearing sediments. Based on the modified Cam-clay model, we have introduced the hydrate saturation and unified hardening parameter to modify the yield function, in order to reflect the impact of methane hydrate on shear strength and dilatancy and softening characteristics. And then, an elastoplastic constitutive model considering the formation and degradation of cementation of the methane hydrate is proposed and the corresponding elastoplastic matrix is derived. Finally, the comparison between the simulation results and the existing triaxial test data shows that the model can predict the strength, dilatancy and softening of the methane hydrate bearing sediments well, and the rationality and validity of the model are verified.