The invention relates to application of high-tacticity trapezoidal polyphenyl silsesquioxane in flame retardant polycarbonate, which belongs to the technical field of flame retardancy. The application comprises the following steps of: drying the high-tacticity trapezoidal polyphenyl silsesquioxane and polycarbonate; then placing the high-tacticity trapezoidal polyphenyl silsesquioxane, the polycarbonate and a processing auxiliary agent into blending equipment for blending to obtain a mixed material; fusing, blending and granulating the obtained mixed material in a double-screw extruder to obtain a blend of the high-tacticity trapezoidal polyphenyl silsesquioxane flame retardant polycarbonate; and drying and injecting for moulding. The invention provides an environmental-friendly type flame retardant polycarbonate; after drying and injecting for moulding, a UL-94 combustion grade reaches 0.8mm V-0 grade at maximum, and an oxygen index reaches 51 percent at maximum; the total smoke yield is reduced; when the adding amount of the high-tacticity trapezoidal polyphenyl silsesquioxane is 8 percent, the highest heat release rate of the polycarbonate can be reduced to 152.8kW/m<2>; and when the adding amount is smaller than 12 percent, the high-tacticity trapezoidal polyphenyl silsesquioxane less influences or grains the mechanical performance of polycarbonate.