In this paper, the polypropylene was functionalized by isocyanate silane coupling agent grafted polypropylene (IS-g-PP), various characterization methods were conducted to evaluate the interfacial compatibility of WF/PP. The results indicated that IS-g-PP remarkably enhanced the interfacial adhesion between WF and PP with improved mechanical property, tensile strength was improved by 96.1%, and flexural strength was also increased apparently. According to the DSC results, the crystallization temperature of PP was decreased due to its enhanced interfacial adhesion. Most importantly, the use of IS-g-PP reinforced the storage modulus, loss modulus, and complex viscosity of WF/PP. These results demonstrated that IS-g-PP enhanced the interfacial interaction, and the mobility of PP chain was restrained, and was further confirmed by SEM analysis.