The invention discloses an outdoor overhead ageing-resistant insulating polyolefin cable material and a preparation method thereof. The outdoor overhead ageing-resistant insulating polyolefin cable material comprises, by weight, 60-80 parts of ethylene-vinyl acetate copolymer, 30-40 parts of chlorosulphonated polyethylene, 4-6 parts of isopropyl phenyl diphenyl phosphate, 4-5 parts of acetyl tri-n-butyl citrate, 8-10 parts of magnesium hydroxide, 40-50 parts of di-iso-decylphthalate, 6-8 parts of butadiene triethoxy silane, 2-4 parts of organic chromium complex, 6-8 parts of lead sulfate tribasic, 5-7 parts of p-phenylenediamine, 30-40 parts of nano calcium carbonate, 6-10 parts of beta-diketone, 12-14 parts of ammonium polyphosphate, 7-8 parts of silicone emulsion, 5-7 parts of fluoro-alkyl polyether modified polysiloxane, 7-9 parts of zinc stearate, 5-8 parts of nano calcium superoxide, 6-9 parts of paraffin and 8-12 parts of hexadecyl dimethyl amine. According to the outdoor overhead ageing-resistant insulating polyolefin cable material and the preparation method thereof, the added di-iso-decylphthalate plasticizer and the ethylene-vinyl acetate copolymer are matched, in this way, the aging resistance is improved, the processability is also improved, and the flexibility of a cable is improved; meanwhile, the ammonium polyphosphate has the condensation and phase neutralizing functions, and an extremely good frame retardant effect is achieved through the combination of the ammonium polyphosphate and the magnesium hydrate; the added chlorosulphonated polyethylene has the wear resistance, electric insulation resistance and other characteristics.