Relating to the technical field of high polymer sealing material preparation, the invention relates to a flame retardant polysulfide sealant and its preparation process. The sealant comprises component A, a main gum material, and component B, a curing agent. The component A comprises liquid polysulfide original gum, white carbon black, activated calcium carbonate, calcium carbonate, aluminum hydroxide, antioxidant 2, 6 di-tert-butyl p-methylphenol, chlorinated paraffin, a phosphate flame retardant, a dibutyl phthalate solution of phenolic resin, epoxy resin, and other flame retardant; and then component A and component B are fully mixed to obtain the sealant. The preparation process of the invention is simple and has a unique principle. The prepared product not only has a good flame retarding effect, and at the same time has superior corrosion resistance to acid, alkali, salt, oil, and other organic solvents as well as aging resistance. With good elasticity, strength, and extensibility, the prepared polysulfide sealant does not flow under high temperature and does not fracture under low temperature. Characterized by no toxicity, no pollution, and long service life, the polysulfide sealant of the invention is convenient for construction, and has a low cost as well as a wide application range.