The invention relates to a PC/PMMA alloy and a preparation method thereof. The PC/PMMA alloy comprises the following components by weight percent: 75-82% of PC, 10-15% of PMMA, 4-10% of toughener, 3-5% of compatibilizer and 1-2% of antioxidant. The PC/PMMA alloy has the advantages of good mold filling flowability, excellent processing performance, high impact resistance, chemical resistance, highhardness and difficult scratching, and can adjust the transmittance of the PC/PMMA and the surface pearlescent color according to the needs, and be used as housings of communication devices with higher surface hardness and used for packaging foods with higher requirements on the surface luster.