A series of epoxy (EP) resin-based composites were prepared using a magnetically responsive cobalt@graphene nanoplatelet (Co@GNP) as thermally conductive and electromagnetic shielding reinforcing fillers by the introduction of catalytic sites and coprecipitation techniques. Our findings suggested that the formation of the network structure between Co@GNP and Co@GNP made the resultant composites exhibit excellent heat transfer/heat dissipation efficiency and stability at elevated temperatures. Furthermore, the method of systematically solving and predicting heat transfer efficiency of resultant composites was proposed with the aid of the TPM (three-parameter fitting method), FPM (four-parameter fitting method), and ETM (enthalpy transformation method). The correlation between calculated results and experimental data was compared and analyzed, with the positive influence of filler loading and magnetic field orientation on the thermal conduction of the composites verified. At the same time, the obtained samples also showed acceptable electromagnetic interference shielding effectiveness (EMI SE) within the X-band. The present work has practical implications for further expanding the application ranges of EP/Co@GNP composites, which also provides insight into the optimal design of manufacturing routes for polymer composites with desired performance.