The invention discloses a polystyrene foaming material and a preparation method thereof, wherein the polystyrene foaming material comprises, by weight, 90-105 parts of modified polystyrene, 2-7.5 parts of a reinforcing agent, 0.5-10 parts of a flame retardant, 0.5-5 parts of a foaming agent, 0.1-1 part of a stabilizer, and 0.5-2 parts of perfluorohexanone. According to the present invention, by adding the perfluorohexanone, the effect of the foaming agent can be provided to a certain extent by using the characteristic of easy vaporization of the perfluorohexanone, and the perfluorohexanone canimprove the flame retardant property of the polystyrene foaming material and reduce the adding amount of the flame retardant, and can be remained in the closed gas pores of the molded polystyrene foaming material so as to improve the thermal insulation effect, such that the synergistic effect is obvious; the preparation method has characteristics of simpleness, stability, easily-available raw materials, low cost and important promotion value; and the product has advantages of excellent density, excellent mechanical property, excellent thermal insulation performance and excellent flame retardant performance, has comprehensive performance obviously superior to the similar products on the market, and can be widely used.