In this work, WPU/GO modified by DA (DGO) composites were successfully fabricated via in situ polymerization and effects of DGO on WPU performance were further investigated. It was found that the addition of DGO significantly improves the thermal stability and mechanical properties of WPU/DGO composites. Especially when the concentration of DGO is 1 wt.%, the tensile strength and Young's modulus of the WPU/DGO composites are increased by 98% and 124%, respectively, compared with pure WPU. It has been confirmed that GO is coated by DA through dual effects of covalent bonding and physical adhesion, indicating that the surface of DGO contains highly reactive functional groups such as catechol, amino, imine and hydroxyl groups. This can enhance the interfacial adhesion between GO and WPU, which can significantly improve the mechanical properties of WPU. Meanwhile, the addition of DGO effectively inhibit the UV oxidation degradation behavior of WPU. This is due to DGO endowed with ultraviolet absorption capability and radical trapping ability by polymerization of DA into PDA on the surface of GO.