In this study, waterborne polyurethane (WPU), a novel modifier, was used for the wet surface modification of talc, and its mechanism was investigated. Polypropylene (PP)-based composites with modified talc were synthesized and subjected to an examination of their mechanical properties. The wetting contact angle demonstrated that the modified talc exhibited an excellent modification effect at a specific amount of modifier (2.0 wt.%). The X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) results indicated the successful coating of WPU on the surface of the talc particles. SEM images revealed that modified talc displayed improved wettability, compatibility, and dispersion in PP/talc + WPU composites. The mechanical properties results showed that the PP/talc + WPU composites ensured superior comprehensive properties with a flexural strength of 55.9 MPa, impact strength of 4.72 kJ/m2, tensile strength of 34.8 MPa, and elongation of breaks of 32.4%. The incorporation of WPU-modified talc into plastic materials has been synthesized to leverage its beneficial properties, leading to reduced production costs and improved performance and functionality of the final product.