The invention discloses a composite insulator umbrella skirt material and a preparation method thereof, and relates to umbrella skirt materials of power transmission line composite insulators. The material comprises the following raw materials: ethylene propylene terpolymer, natural rubber, modified mica powder, polyphenylene oxide resin, calcined bauxite, silicone oil, N-hydroxymethyl acrylamide,an antiager, a coupling agent, a plasticizer and an accelerant. The preparation method comprises the steps of banburying on the raw materials, vulcanization and open milling. The composite insulatorumbrella skirt material is simple to prepare, wide in material source, low in cost, and excellent in comprehensive performance, has the characteristics of high electrical insulating property, good mechanical property and stable physical and chemical properties, is antioxygenic and ageing resistant, effectively prolongs the service life of a product, and has a good market prospect.