Abstract: Reactive halogen-free flame retardant composite (OP-FRC) was prepared by compounding unsaturated polyester oligomer (UPEO) with inorganic flame retardants, and then OP-FRC was introduced into ethylene-vinyl acetate copolymer (EVA) -based low-smoke halogen-free flame retardant cable sheath material by melt blending. Effects of UPEO on structure and properties of composites was investigated using thermogravimetric analyzer, differential scanning calorimeter, parallel plate rheometer, electronic universal testing machine, scanning electron microscope, and limit oxygen index tester. Results showed that incorporation of UPEO in OP-FRC could improve dispersion of inorganic flame retardants in EVA-based, enhance interaction between inorganic flame retardants and EVA-based, facilitate formation of inorganic filler network, increase mobility of molecular segments, promote relaxation of entangled matrix structure, finally improve fatigue resistance, thermal stability and crystallization ability of composites. When mass fraction of UPEO was 4%, elongation at break of composites was 215.5%, fatigue life was 26 354 times, and limiting oxygen index (LOI) was 31.5%.