Abstract: Nano sepiolite was used as a synergist to prepare flame-retardant ethylene vinyl acetate copolymer (EVA) composite materials. Influence of nano sepiolite on the mechanical, thermal, and flame retardant properties of magnesium phosphorus flame retardant EVA was studied through hardness, tensile testing, thermogravimetric analysis (TGA), oxygen index (LOI), and cone calorimeter testing. Hardness test results indicated that as the content of sepiolite increases, hardness showed an upward trend. Tensile performance results showed that with the increase of sepiolite content, tensile strength decreased, and the elongation first increased and then decreased. Volume resistivity test results showed that with the addition of nano sepiolite, the volume resistivity of composite material increased, while when the amount of nano sepiolite added was less than 2 g, the volume resistivity of EVA composite material sharply decreased.In terms of thermal performance, as the amount of nano sepiolite added increased, the initial melting temperature, melting peak, crystallization temperature, and crystallinity of the sample first increased and then decreased;There were three stages of weight loss during the heating process, and the temperature of the first decomposition peak changed slightly when the amount of nano sepiolite added was less than 2 g; When the amount of nano sepiolite added was greater than 2 g, the decrease was significant; As the amount of sepiolite added increases, the temperature of the second decomposition peak decreased from 383.8 ℃ to 375.9 ℃, while the temperature of the third decomposition peak remained basically unchanged. The results of the Limiting Oxygen Index (LOI) test showed that with the amount of sepiolite added, the LOI gradually increased, rising from 32.7% to 34.7%. The results of the cone calorimeter test indicated that an appropriate amount of nano sepiolite can effectively reduce fire behavior parameters, such as heat release rate (HRR), total heat (THR), total smoke release (TSP), and mass loss rate (MLR). The photos of ashes indicated that when the amount of sepiolite added was 2 g can form a dense crust layer with flame retardants, thereby hindering the spread of flames inward.