Epoxy resin (ER) is one of the most widely used synthetic resins, and the improvement of its toughness is an important issue. In this study, Epon 828 is used as ER resin, polytetramethylene ether glycol (PTMG) and liquefied wood (LW) are used as polyol, and IPDI, H12‐MDI, Desmodur N, and Desmodur L are used as isocyanate. The influence of polyurethane resin (PU) composition on the reactivity of ER/polyol/isocyanate blended resin and the properties of ER/PU composite are investigated. The results show that the mixture of ER/PTMG/IPDI has greater reactivity, followed by ER/PTMG/Desmodur N, while ER/PTMG/Desmodur L has lower reactivity. In the structure of ER/PU blended resin composites, ER and PU resins not only form a physical interpenetrating structure, but also undergo a copolymerization crosslinking reaction. The modulus of elasticity of ER/PU composites prepared with trifunctional Desmodur L and Desmodur N is greater than that of bifunctional IPDI and H12‐MDI, while those with LW as polyol is greater than that of PTMG as the raw material. Different polyols (PTMG and LW) and isocyanate (IPDI, H12‐MDI, Desmodur N, and Desmodur L) are added directly to epoxy resin, the reactivity of epoxy/polyol/isocyanate blended resins and the properties of ER/PU composites are investigated. The results show that the ER resin and the PU not only form a physical interpenetrating structure, but also undergo a copolymerization crosslinking reaction.