The hexagonal boron nitride nano-sheets (h-BNNSs), as grapheme-like two-dimensional flaky nanomaterial, is able to not only significantly improve thermal conductivity of polymer materials with a low loading content, but also keep excellent electrical insulation property of materials. The interlayer acting force of boron nitride is far stronger than that of grapheme. Therefore, the preparation of nano-sheets by liquid phase exfoliation of hexagonal boron nitride powder has more practice significance. This paper presented six liquid phase exfoliation methods of h-BNNSs and its exfoliation mechanisms, and introduced properties of the composites (e.g. heat-conducting property, transparency, mechanical property and magnetism, etc) prepared by h-BNNSs, expecting to be helpful for development of heat-conducting polymer matrix composites.