AbstractHigh thermal conductivity and electrical insulation materials are necessary for packaging materials of miniaturized electronic equipment at present. Graphene nanosheets (GNs) have great potential in polymer composites due to its excellent thermal conductivity. However, the ultra‐high conductivity of GNs will reduce the insulation of polymer composites, so that the GN composites have good thermal conductivity and electrical insulation has become the focus of research. Herein, the closed cell polystyrene nanocomposites are polymerized by using a Pickering emulsion route. Based on the exfoliating effect of pristine graphite at the oil–water interface and the amphiphilic properties of GNs during the preparation of emulsion, the resulting graphite can achieve good dispersion in the polystyrene resin. Furthermore, the high heat transfer rate of the resulting graphite makes the temperature of polystyrene resin increase by 60.2°C at room temperature within 1 min. Meanwhile, the high volume electrical resistivity (3.63 × 109 Ω·m) and breakdown strength (33.8 kV·mm−1) confirms the PNGL0.610%/PS composite keep excellent electrical insulation at 10.0 wt% filler loading.