The invention discloses a moldproof polyethylene sheath material for cables and a preparation method thereof. The moldproof polyethylene sheath material for cables is prepared from the following raw materials in parts by weight: 80-90 parts of linear low density polyethylene, 15-20 parts of chlorosulfonated polyethylene, 10-15 parts of poly(4-methyl-1-pentene), 20-30 parts of carbon black N660, 4-8 parts of turpentine, 5-10 parts of dioctyl terephthalate, 1-2 parts of anilinomethyl triethoxy silane, 3-5 parts of methyl p-hydroxybenzoate, 8-12 parts of decabromodiphenyl oxide, 5-10 parts of zinc borate, 10-15 parts of aluminum hydroxide, 4-8 parts of brucite powder, 5-10 parts of tri(2-chloropropyl)phosphate, 2-4 parts of light magnesium oxide, 1-2 parts of tributyltin chloride, 2-3 parts of barium stearate, 3-6 parts of calcium hydroxide, 3-4 parts of oxidized polyethylene wax, 5-8 parts of quartz powder, 3-5 parts of nano silver and 4-6 parts of composite filler. On the premise that the excellent moldproof function of the sheath material is ensured, the sheath material can effectively inhibit Aspergillus niger, Aspergillus terreus and other molds from growth and reproduction, so that the cable is free from mold invasion, and the service life of the sheath is prolonged.