The invention discloses nanoscale flame retardant reinforced polycarbonate and a preparation method. The nanoscale flame retardant reinforced polycarbonate comprises the following components by mass: 60%-85% of polycarbonate, 5%-15% of nano carbon fiber, 10%-15% of a nano flame retardant agent, 4%-8% of an organosilicone flame retardant agent, 0.5%-2% of a coupling agent, 1%-3% of a compatibilizer, 0.1%-1% of an antioxidant and 0.1%-1% of a lubricant. The beneficial effect is in that, compared with the prior art, the prepared nanoscale flame retardant reinforced polycarbonate has the characteristics of high strength, good rigidity, heat resistance, excellent dimensional stability, high flame retardant efficiency and the like, can reach UL94V-0-level flame retardant property, has good processing property, excellent electrical performance and strong high temperature corrosion resistance, and has very broad application prospects in automotive, chemical, mechanical, electrical, construction and other fields as high performance structure materials.