In this study, we suggest to fabricate high strength lightweight 3D porous structure based on polymer-metal composite using directional freeze-drying method. Ultralight cellulose nanofiber (CNF) reinforced with silver nanowire (AgNW) 3D porous structure was fabricated using one-step process of directional freeze-drying method. The strength of AgNW/CNF 3D porous structure increased by 14.3 times even when the relative density of the Ag nanowire increased by 0.29%. As the concentration of Ag nanowire increases, the stretch-dominant deformation property of AgNW/CNF 3D structure gradually increses. Metal coated polymer 3D porous structure was fabricated using copper electroless plating on the polyvinylalcohol (PVA) directional freeze-drying 3D structure. Sn-Ag activation condition for Cu electroless plating on non-conductive polymer was determined. Mechanical strength of Cu/PVA 3D structure was lower than expected because of tearing of copper coating layer. Further studies are needed to increase connectivity between metal and polymer to solve this problem.