Abstract: The filling modification and blending modification of polymers were important methods for the high performance of general plastics. Interfacial compatibility was a common problem in polymer modification. How to improve the interfacial compatibility of composites and explore the correlation between interfacial compatibility and Poisson's ratio are still important topics in polymer modification. Ternary monomer graft polypropylene (GPP) was prepared by solid phase method and blended with glass fiber and polypropylene to prepare polypropylene/glass fiber composites. The structure and properties of the composites were characterized by video extensometer, differential scanning calorimetry, scanning electron microscopy, infrared spectroscopy, dynamic rheological test and universal tensile test. The results show that the addition of GPP compatibilizer improve the interfacial strength of polypropylene-glass fiber composites. With the increase of GPP compatibilizer, the storage modulus (G') and loss modulus (G'') are both increasing, and the increase of G' is greater than that of G''. Therefore, the elastic behavior of the composite system is significantly greater than that of the viscous behavior. The mechanical properties of polypropylene-glass fiber composite with 7wt% GPP are the best, which was verified by Cole-Cole curve. The results of infrared spectroscopy and scanning electron microscopy show that the GPP compatibilizer form an interfacial layer with the glass fiber, which improve the interfacial compatibility between the resin and the glass fiber and enhance the stress transfer of the glass fiber in the polypropylene matrix. GPP was used as a modifier to improve the interfacial compatibility of PP-GF composites. As a modifier to improve the interfacial compatibility of PP-GF composites, larger transverse strain and smaller Poisson's ratio are formed during the tensile process, which improve the mechanical properties of the composites.