p-Hydroxybenzoic acid grafted oligochitosan (p-HBzA-g-OCS) was obtained by the graft copolymerization of p-hydroxybenzoic acid (p-HBzA) and oligochitosan (OCS). The waterborne polyurethane modified by p-HBzA-g-OCS (HOCS-WPU) was prepared reacting p-HBzA-g-OCS as a crosslinker with polyurethane prepolymer (PPU). The structure of samples was confirmed by FTIR and UV-Vis, its properties were analyzed by DLS, mechanical properties, XRD, TGA and radical scavenging assay of ABTS and DPPH. The results showed that a smaller particle size of HOCS-WPU emulsion was 57.85 nm. Compared to the unmodified WPU, the tensile strength of the film increased from 14.03 MPa to 16.85 MPa, the crystallinity of the polyurethane declined from 3.57% to 3.45%, and the initial decomposition temperature increased from 204.6 ℃ to 216.7 ℃ when 2% of p-HBzA-g-OCS (based on the total mass of the synthetic PPU starting materials) was added. The free radical scavenging assay results showed that ABTS and DPPH radical scavenging assay of HOCS-WPU reached 62% and 35% when the mass concentration of the polymer was 2.5 g/L. The antioxidant activity of HOCS-WPU was significantly better than that of the unmodified WPU.