Sand production can yield severe operational issues during natural gas hydrate (NGH) exploitation. As a prerequisite for effective sand control design, a reliable simulation approach is required to predict sand production rate of the unconsolidated sediment after hydrate decomposition. In the present study, a quantitative model to predict fluid-driven sand discharge rate has been proposed by assuming an imaginary free fall arch (FFA) region at the gravel pack interface. Through integrating the FFA particle discharge model, critical remigration velocity model, and sand erosion model, a novel simulation approach is developed to determine the time-dependent permeability change of the sanding sediment during depressurization-induced hydrate exploitation. The numerical model was verified through comparison against the flooding experiments with both single opening and gravel pack. A sensitivity analysis was carried out to study parameters (such as packed gravel size, sand particle size, opening blockage, and hydrate reformation) that may affect the sanding rate and permeability distribution within the unconsolidated sediment as well. By utilizing the simulation approach proposed in this paper, the sand intrusion within the gravel pack and the permeability variation of the unconsolidated sediment can be obtained in a computationally efficient way, which is of significance in sand control design and potential geological risk identification during hydrate exploitation.