Flexible polyurethane foam (FPUF) has many advantages such as lightweight, low density and high specific strength and is widely used in furniture, automobile industry, construction and transportation. However, FPUF is extremely flammable in the air, and a large amount of toxic gas will be generated when it is burned. The fire protection technology of FPUF has attracted more and more attention. Generally, it is an effective method to improve fire protection of FPUF by introducing additive flame retardant. As a relatively new approach, layer-by-layer (LBL) self-assembly technology is widely used in research fields such as biology, materials and nanoscience. In this work, the research and application of LBL self-assembly technology in the field of flame-retardant FPUF were described, and zero-dimensional, one-dimensional, two-dimensional nanomaterials, one- and two-dimensional nanocomposites systems and other self-assembly systems in flame-retardant FPUF were introduced in detail. The flame-retardant mechanism of flame-retardant FPUF systems was also systematically analyzed, and finally, the development of LBL self-assembly technology in flame-retardant FPUF was prospected.