The invention relates to a high pressure resistance irradiation crosslinking environment-friendly and flame-retardant rubber and plastic composite material and a preparation method thereof. A formula of the composite material comprises raw materials in parts by weight: 15 to 45 parts of high-density polyethylene, 25 to 50 parts of elastomer resin, 10 to 30 parts of EBA, 5 to 25 parts of flexibilizer, 60 to 100 parts of flame retardant, 0.8 to 2 parts of antioxidant, 1 to 2 parts of lubricant, 0.03 to 0.1 part of crosslinking agent and 1 to 2.5 parts of crosslinking sensitizer, wherein the elastomer resin is prepared from polyurethane elastomer and ethylene propylene diene monomer elastomer, and a mass ratio of the polyurethane elastomer to the ethylene propylene diene monomer elastomer is 1 to (1 to 3). According to the composite material disclosed by the invention, the formula is improved; for example, the polyurethane elastomer and the ethylene propylene diene monomer elastomer are utilized as the elasomer resin, the high-density polyethylene and the EBA are added, meanwhile the matters of the flexibilizer, the flame retardant, the antioxidant and the like are added in an auxiliary mode; thus, the composite material disclosed by the invention has excellent wear resistance, flame resistance and heat resistance, a higher gel content can be obtained, and a pressure-resistant requirement of the material in a high-temperature welding process is met.