Polyethylene glycol (PEG) has been regarded as a promising thermal management material for next-generation building materials due to its high energy storage density and phase change performance. However, its practical application has been limited by some issues such as easily leakage and low thermal conductivity. In this work, a high-thermal-conductivity wood-based composite phase change material (Cu-DW/PEG) was fabricated by impregnating copper (Cu) precursor solution and PEG into delignified wood (DW). The incorporation of Cu nanoparticles increased the thermal conductivity of Cu-DW/PEG by 105 % and 64 % compared to pure PEG and DW/PEG composite, respectively. This also endow the Cu-DW/PEG good photo-thermal conversion capability, achieving a conversion efficiency of 76.5 %. Meanwhile, the Cu-DW/PEG exhibits relatively high latent heat (132.93 J/g), good shape stability and thermal cycling stability. Considering these excellent performances, the Cu-DW/PEG is a promising material for thermal management, building energy conservation, and solar thermal harvesting.