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The Korea Institute of Geoscience and Mineral Resources conducted depressurization experiments at various gas hydrate saturation conditions, using mini pressure cells, to determine critical gas hydrate saturation. Their results indicated that it is necessary to carry out a numerical simulation in connection with the experiments to determine the critical gas hydrate saturation at numerous conditions that could not be incorporated into the experiments. In this study, a numerical simulation model, which simulated a mini pressure cell, was developed to verify the results of the aforementioned experiments. The changes in the fluid density and computer tomography values showed a similar trend. The validated numerical simulation model was used to determine the dissociation behaviors and productivities for various gas hydrate saturation levels (10–80%). As the gas hydrate saturation increased, the fluid permeability decreased. The gas hydrate dissociation was slowed by this correlation, and the production of gas and water was delayed at 50–60% gas hydrate saturation. Thus, the critical gas hydrate saturation was determined to be 50–60% for the experimental conditions of the field production test at the Ulleung Basin, East Sea, Korea. A pressure difference was noticed between the production and injection points due to the pressure propagation being delayed at critical gas hydrate saturation. Verifying the results of the experiments proved useful to understanding the dissociation and multiphase flow patterns in various depressurization scenarios.