The invention relates to product formula and preparation method of a flame-proof ABS. Wherein, the formula comprises mainly: ABS resin, antimony trioxide, decabromodiphenyl oxide, coupling-treated aluminum hydroxide, anti-oxidant 168, tricresyl phosphate, chlorinated polyethylene (CPE), polyvinyl chloride (PVC), EBS, magnesium stearate, SBS, nano-SiO2, and zinc borate. The preparation method comprises: mixing the ABS resin and tricresyl phosphate in high-speed mixer, adding other materials; putting into double screw extruder; cooling, granulating, screening, drying, and packaging. This product has well properties with low cost.