Boron nitride nanosheets (BNNSs), as a two-dimensional flake nano material, has high thermal conductivity and thermal stability. The thermal conductivity of the composites can be improved by adding boron nitride nanosheets as a filler. Based on the research progress on the thermal conductivity of composites modified with boron nitride nanosheets in recent years, the preparation and modification methods of BNNSs and the establishment of thermal conductivity paths are summarized. Subsequently, the thermal conductivity mechanism of composites was introduced and the affecting factors of the thermal conductivity of the composites were analyzed. Finally, the improvement of thermal conductivity of composites was prospected.