Abstract: The flame-retardant polycarbonates (PC) were prepared by mixing the PC with different compounded flame retardants which were obtained by separately mixing the polyborosiloxane (PB) with three types of organophosphate (OPP). The synergistic effect of PB on OPP/PC system was evaluated using limited oxygen index (LOI) and cone calorimeter analysis. The results show that, at 5% mass fraction of total flame retardant addition, the compounded flame retardant with above 1.25% mass fraction of PB can improve the LOI of the PB-OPP/PC system. PB flame retardant promotes the char formation during the combustion of the PB-OPP/PC, which reduces the emission of the smoke, heat and CO. The total smoke release decreases by 31.8% to 51.0% when each of the three compounded flame retardants is added into PC. The combustion process is moderated and the hazard of fire is reduced. It is also found that the moderate addition of PB improves the tensile strength, flexural strength, vicat temperature and the transparency of PB-OPP/PC.