The invention discloses a preparation method of an improved EPDM (Ethylene-Propylene-Diene Monomer) cable sheath material. The method comprises the following steps: mixing EPDM, chloroprene rubber, polypropylene and maleic anhydride grafted polypropylene to obtain a first rubber compound; adding montmorillonoid, nano aluminium nitride, barium sulfate and pre-dispersed phenolic aldehyde hollow microspheres to the first rubber compound, and mixing for 1 to 5 minutes; then adding 5, 5'-dimethyl-5, 10-dihydracridine, N'-(1, 3-dimethylbutyl)-N'-phenylenediamine, an age resister 2246, N-phenyl-naphthylamine, polybutylated bisphenol A, tri(nonylphenyl) phosphite, isproportionated potassium rosinate, vitamin C and pentaerythritol, and mixing for 2 to 5 minutes; adding stearic acid, a plasticizer TP-759, butylmercaptooxo stannane, phenolic resin, tin( II) chloride dehydrate, octadecylamine and an accelerant, and mixing for 3 to 8 minutes; performing thin-passing to obtain a second rubber compound; vulcanizing the second rubber compound to obtain the EPDM cable sheath material.