Based on chemical grafting method and melt blending method, halogenated phosphate ester-polystyrene-zinc borate (TDCPP-RPS-ZB) composite building material was prepared with recycled polystyrene (RPS) as material base, halogenated phosphate ester (TDCPP) as flame retardant and zinc borate (ZB) as smoke suppression material. Surface functional groups, mechanical properties and flame retardancy of the composites were analyzed. The results of surface functional group analysis showed that TDCPP and ZB were successfully mixed into the RPS substrate after chemical grafting and melt blending. The results of mechanical properties analysis showed that the apparent density and impact strength of the RPS matrix were increased by 29.36% and 33.33%, respectively, and the tensile strength was decreased by 13.39%. According to the results of flame retardancy analysis, with the addition of TDCPP and ZB with different mass fractions, the oxygen index of TDCPP-RPS-ZB composite was increased to 25.4%, 30.1%, 31.2% and 32.4%, respectively. The thermal stability is improved, the peak combustion rate decreases and the total heat release decreases slightly during the combustion process, and the vertical combustion grade can reach V-1 rating. In addition, the smoke production of RPS decreased from 39.4 m² to 33.1, 28.1, 31.0, 21.8 m² after adding TDCPP and different mass fractions of ZB, indicating that the addition of ZB can significantly reduce the smoke production of material combustion.