Sanding is vitally a serious problem during heavy-oil production from unconsolidated reservoirs. In order to effective sand control and high well production, various sand exclusion technologies are used for horizontal well completion, especially, the open-hole gravel pack (OHGP) has been widely used. So it is critical to quantitatively evaluate permeability impairment because of sand particulates migration and plugging in gravel-packed layer, and it is also important to predict horizontal well productivity. In this paper, we have developed one numerical model of permeability impairment based on the previous experimental observation. This numerical model considers the liquid-solid fluid flow process, and sand particles depositing and plugging in gravel-packed layer. The numerical simulation results of permeability impairment at different sand volume fraction, fluid viscosity and sand radius are given, and the simulated results are in good agreement with the previous experimental results.Integrating the permeability impairment model a new model to predict productivity of gravel-packed horizontal well has been proposed. The proposed model couples reservoir inflow and seepage in gravel layer, and it can quantitatively evaluate the damage of gravel layer and predict well productivity performance. The numerical simulation of real-world scenarios investigates that it is more accurate than previous models, and it is very easy to use.