Abstract: Polyurethane has excellent physical and mechanical properties, and is widely used in leather, functional materials and medical fields. However, polyurethane is prone to combustion, so the introduction of nanomaterials with flame-retardant function in polyurethane is of great significance to improve the fire safety of polyurethane materials. This review first summarized the advantages of nanomaterials over traditional flame retardants. The development of flame-retardant polyurethane nanocomposites in terms of preparation, mechanism, and applications in leather and functional materials was demonstrated in this review. We also discussed the introduction of various types of nanomaterials, e.g., carbon nanotubes, metal-organic frameworks, and MXene. Meanwhile, research and development direction of the flame-retardant polyurethane nanocomposites was discussed.