The two-stage gravel-packing technique has been widely adopted in the development of unconsolidated sandstone reservoirs with high sanding rates and silt contents. Compared with the traditional gravel-packing operation, the lifespan and long-term conductivity of the two-stage gravel pack improve significantly. In the present study, an experimental study was undertaken to determine the dynamic permeability change of two-stage gravel packs during sand production. Thirty-nine groups of flooding tests were carried out with various experimental settings, and the pressure drop of each section (i.e., the sanding section, gravel bed I, and gravel bed II) was monitored dynamically during flooding. The permeability characteristics of each section were used to determine the mechanisms of sanding, pore blockage, and particle remigration under different packing arrangements. Using the proposed experimental setup, a sensitivity analysis was carried out to study the parameters that may affect the permeability of the sand pack, such as the two-stage gravel size, packing length, flooding rate, and silty sand content. Based on the observed permeability recovery phenomena in gravel bed I during the experiments, a dynamic permeability prediction model considering the remigration of deposited particles was proposed. Compared with the traditional deep-bed filtration model and the experimental results, the verification showed that the new model is more suitable for predicting the dynamic permeability of two-stage gravel packs.