The invention relates to a copolymer compatilizer applied in the composite ABS and a composite composed of the compatilizer, ABS and thermoplastic resin. The copolymer compatilizer is a tetrabasic random copolymer, and which is polymerized by the aromatic series vinyl monomer, the cyaniding vinyl monomer, the Alpha, Beta-unsaturated dicarboxylic anhydride monomer and the Alpha, Beta -unsaturated fatty acid monomer and the polymerized, and through the mass polymerization, Solution Polymerization or emulsion polymerization. When the random copolymer is as a compatilizer applied in the composite comprised of ABS and polyamide, polyimide, polycarbonate, polyester, biodegradable polyesters, polyformaldehyde, polymethyl methacrylate or fibrin, the resistance of the composite, stability of the melt and process ability can be greatly improved.