Abstract: Natural gas hydrates existing in sandy reservoirs are easier to extract than natural gas hydrates existing in viscous clay layers. Accurately simulating the mechanical behavior of sandy sediments is crucial for assessing seabed stability and mitigating geological risks, such as submarine landslides, during hydrate extraction. However, constitutive models that account for the decomposition of gas hydrates in sandy sediments are still underdeveloped. This study presents a critical state model tailored for hydrate-bearing sandy sediments, based on the stress distribution concept and on the SANISAND model framework. By incorporating stress distribution to represent the role of hydrates in the sediment matrix, the model captures the impact of hydrates on the mechanical behavior of the sediment skeleton. Additionally, hydrate saturation parameters are introduced into the critical state line equation to account for the effects of hydrate filling on the sediment’s shear contraction and dilation behavior. The model proposed can simulate the enhanced shear strength and dilation caused by hydrates, as well as predict the changes in soil mechanical properties due to hydrate decomposition. The model's accuracy is validated by predicting the results of drained triaxial shear tests on hydrate-bearing sandy sediments in laboratory conditions.