The invention relates to a calcium sulfate whisker modified polystyrene composite material, and a preparation method thereof. The calcium sulfate whisker modified polystyrene composite material is prepared from the raw materials of, by weight: 100 parts of polystyrene, 10 to 40 parts of calcium sulfate whisker, 10 to 20 parts of styrene-butadiene block copolymer, 0.1 to 0.3 parts of anti-oxidant 1010, 0.1 to 1 parts of zinc stearate, and 1 to 3 parts of titanate coupling agent. The preparation method comprises the steps that: calcium sulfate whisker and titanate coupling agent are added into a high-speed mixer, and are mixed for 5 to 10 min; rest raw materials are added to the obtained modified calcium sulfate whisker, and the mixture is mixed for 5 to 10 min in the high-speed mixer; the obtained mixture is extruded and granulated by a double-screw extruder. The calcium sulfate whisker modified polystyrene composite material has good impact resistance and heat resistance. Therefore, the material is suitable to be applied in the manufacturing of electric appliance housings with strict requirements of impact resistance and heat resistance.