Weathering of wood-plastic composite (WPC) leads to discoloration and cracks, which greatly limits its outdoor application. In this study, light stabilizers (including UV-327, HS-944, and Nano-SiO2) were added to the shell of coextruded high-density polyethylene (HDPE) based WPC to improve its anti-ultraviolet (UV) aging property and simultaneously to maintain its good mechanical property. The obtained results showed that the UV-327 was the most effective light stabilizer on improving the mechanical and anti-UV aging properties of the composites among the three stabilizers used. WPC samples added with 2% UV-327 had the highest retention rates in flexural strength and also had the smoothest surface after 2500h of UV aging. The samples added with 2% UV-327 had the best protection for the discoloration, showing the lowest values of ΔE (color difference) and ΔL (luminescence) in all samples after 2500h of UV aging. WPC added with 2% UV-327 was oxidized to the slightest extent after 2500h of UV aging. The results reported herein serve to enhance the understanding of the efficiency of light stabilizers in preventing WPCs from UV degradation, with a view toward developing co-extruded WPCs with low cost, high anti-UV aging property and good mechanical property for outdoor applications.