The invention discloses a PMMA/PVC alloy material. The alloy material is prepared from, by weight, 40-60 parts of polymethyl methacrylate, 20-40 parts of polyvinyl chloride, 10-20 parts of brightener, 7-20 parts of fire retardant and 5-10 parts of antistatic agent, wherein styrene-acrylonitrile copolymer serves as the brightener. A method for preparing the alloy material comprises the steps of evenly mixing the formulation constituents in a high-speed mixer at normal temperature, and then conducting extrusion pelletization directly by means of a twin-screw extruder under proper technological conditions. The alloy material has the advantages of being balanced in mechanical property, excellent in weather resistance, resistant to scraping, high in glossiness and resistant to inflaming and static electricity, and is suitable for products including outdoor building materials, electric products and engineering machinery products which have high requirements for weather aging resistance and are resistant to scraping. Compared with a traditional PVC two-stage machine two-step method, the preparing method has the advantages of being simpler and more efficient.