Abstract: The development and preparation of low-cost, defect less and high-efficiency graphene nanoplatelets hybrid flame retardant is of great significance to achieve the multifunctionality of composites. A graphene nanoplatelets hybrid melamine phosphate flame retardant (GMP) with flame retardant and thermal conductivity was prepared by the reaction of powder graphite (GRA) with phosphoric acid liquid phase after mechanical ball milling with melamine as a stripping agent. The morphology, structure, composition and thermal stability of GMP were characterized. The flame retardant, thermal decomposition and thermal conductivity of GMP epoxy resin (EP) composites were studied. Thermogravimetric analysis show that the initial decomposition temperature of GMP increases 29.3℃ from melamine phosphate (MP), which matches more with EP, contributing to the improvement of flame retardant efficiency of this EP composites. The results show that when the addition of GMP reaches 30wt%, EP composites achieve the limit oxygen index of 30.4%, the vertical combustion of UL 94 reached V-0 level, the peak heat release rate (PHRR) decreases by, and the peak smoke release rate (PSPR) decreased by 69% and 74.0% respectively. The thermal conductivity increases to 2.10 W·m⁻¹·K⁻¹, which is increased by 708% compared with EP. This is because the interaction between graphene nanoplatelets (GNPs) and MP in GMP promote the formation of dense expanded carbon layer on EP, which effectively improves the flame retardancy of EP composites. With the increase of GMP content, the thermal conductivity of EP composite is improved by the formation of GNPs and graphite heat transfer channel. The research provides an idea for the design and preparation of graphene nanoplatelets hybrid flame retardants with both flame retardancy and thermal conductivity to solve the fire hazard caused by thermal deposition of EP composites.