Abstract: Glass fiber-reinforced nylon 66 (GF/PA66) composites were prepared using the melt blending method. The composites were characterized by scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), and a universal testing machine to investigate the interfacial mechanical properties. The results reveal that adding nylon powder facilitates the formation of more hydrogen bonds and a small amount of γ-phase, which establishes a dense and uniform network structure on the fiber surface. This improves the interfacial adhesion and enhances the mechanical properties of the GF/PA66 composites. The tensile strength of the composite with 40wt% nylon powder (152 MPa) increases by 72.7% compared to the sample with 0wt% nylon powder (88 MPa). Digital Image Correlation (DIC) data indicate that the synergistic interaction between the glass fibers and the nylon matrix is promoted by the addition of nylon powder, exhibiting typical tensile stress-strain behavior. This study provides a feasible approach for improving the interfacial bonding of modified GF/PA66 composites.