The invention discloses a high-temperature-resistant heat-insulating protective garment and a preparation process thereof, and relates to the field of protective garments, and the high-temperature-resistant heat-insulating protective garment is prepared by selecting a polysulfonamide fabric, performing flame-retardant finishing by using an after-finishing flame retardant, soaking the polysulfonamide fabric in an anti-static liquid, dipping, drying, and coating the surface of the fabric with a polytetrafluoroethylene coating, thereby obtaining the high-temperature-resistant heat-insulating protective garment. The anti-static breathable layer, the heat insulation layer and the flame-retardant layer are sequentially compounded, and the problems that an existing protective garment is poor in heat insulation performance, cannot well block heat energy outside the protective garment and is not ideal in flame-retardant effect are solved; the compounding of organic and inorganic materials can realize complementary advantages, and gives consideration to the mechanical property, weaving property, heat insulation and open fire resistance of polysulfonamide, so that the heat insulation property of the fabric is improved, the flame-retardant layer can prevent combustion products from escaping and inhibit thermal decomposition of materials under the layer, the flame-retardant, low-smoke and low-toxicity effects are achieved, a cracked carbon layer is formed on the surface of the polysulfonamide, and the flame-retardant, flame-retardant and flame-retardant effects are achieved. And the oxidation resistance of the cracked carbon layer is improved, so that the flame-retardant purpose is achieved.