The invention discloses a flame retardant thermal insulation polystyrene material. The raw materials include, by weight, 80-120 parts of styrene, 200-400 parts of water, 80-120 parts of a polyvinyl alcohol solution, 3-5 parts of tricalcium phosphate, 1-1.5 parts of triphenyl phosphate, 2.5-4.5 parts of ammonium polyphosphate, 2-5 parts of silica aerogel, 1-3 parts of di-tert-butyl peroxide, 2-4 parts of water soluble silicone oil, 10-18 parts of pentane, 80-100 parts of a compound flame retardant, 3-6 parts of benzenesulfonyl chloride, 4-6 parts of isopropyl titanate triisostearate, 20-30 parts of fumed silica, 2-3 parts of a rare earth stabilizer, 2-3 parts of a Ca/Zn composite stabilizer, and 3-5 parts of an antioxidant 264. The invention also discloses a preparation method of the flame retardant thermal insulation polystyrene material. The flame retardant thermal insulation polystyrene material provided by the invention has the advantages of simple operation, convenient industrial production, high flame retardance and good thermal insulation performance.