Abstract: Brominated styrene-butadiene rubber (BSBR) was prepared by using dichloroethane as a solvent, SbCl3 as a catalyst and BrCl as a brominating agent. The effect of BrCl dosage on the bromine content of BSBR was investigated. Subsequently, BSBR was mixed with polystyrene by a solution method, and the effect of the bromine content of BSBR on the flame-retardant properties of PS composites was investigated by thermogravimetric analysis, limiting oxygen index (LOI) and cone calorimeter. The results indicated that BSBR achieved a maximum bromine atom percentage of 33.17 % when the dosage of BrCl was set as 70 mL. The introduction of BSBR could effectively improve the flame retardancy of PS. The higher the bromine content in BSBR, the better the flame-retardant effect on PS. As a result, a maximum LOI of 30.8 vol % was achieved for the flame-retardant PS. Moreover, LOI of the flame-retardant PS increased with an increase of BSBR content, but the total heat release of the combustion decreased. In addition, the release amount of CO increased due to incomplete combustion.