The interface plays a key role in determining the properties of polymer composites. However, chemical inertness of hexagonal boron nitride (h-BN) makes its surface modification troublesome. In this study, we, for the first time, used SiO₂ as the modified molecular and investigated the effects of exfoliated h-BN and SiO₂ nanoparticles-modified-exfoliated h-BN (SiO₂@exfoliated h-BN) on the storage modulus, the glass transition temperature, the filler dispersion and the thermal conductivity of polyvinyl alcohol (PVA) composites prepared by a solution mixture method. The results showed that the SiO₂ modification enhanced the interface interaction and improved the performance of the PVA composites. Based on the enhanced interface interaction by SiO₂ modification and the aligned fillers in PVA by vacuum filtration, the high thermal conductivity of 13.88 W/m·K was realized at 15.2 wt% SiO₂@exfoliated h-BN loading. Meanwhile, the tensile strength was also largely improved to 156 MPa, compared with 47 MPa of pure PVA. This study broadens the surface modification method of h-BN and provides a valuable reference for fabrication of high-performance thermal interface materials.