The invention provides a halogen-free flame-retardant sheath material for a class-1E K3 cable used for a nuclear power station. The halogen-free flame-retardant sheath material mainly comprises the following components: ethylene-vinyl acetate copolymer, maleic anhydride-grafted polyolefin, inorganic fire retardant, a synergistic fire retardant, melamine urate, micro-capsulated red phosphorus, an anti-oxidant, an ultraviolet ray absorber, an aqueous graphene solution, a crosslinking sensitizer and a lubricant, wherein the mass percentage of vinyl acetate in the ethylene-vinyl acetate copolymer is about 20 to 40%, a compatilizer is at least one selected from the group consisting of maleic anhydride-grafted ethylene-vinyl acetate copolymer, maleic anhydride-grafted ethylene-octylene copolymer and maleic anhydride-grafted polyethylene, and the ultraviolet ray absorber is at least one selected from the group consisting of 2-(2'-hydroxy-3',5'-di-tert-pentyl-phenyl)benzotriazole and 2-(2'-hydroxy-3',5'-tert-octyl-phenyl)benzotriazole. The halogen-free flame-retardant sheath material has good flame retardation performance, oil resistance, electrical performance and mechanical performance and can meet the requirement on a generation-III nuclear power station for service life of 60 years.