Abstract: Flexible polyurethane foam is widely used as cushions for airplanes and car seats, as well as furniture. However, it is of high flammability and fire risk because of its low decomposition temperature, high hydrocarbon content, and high porosity. In addition, the burning of flexible polyurethane foam results in a very high heat release. It is a big challenge to simultaneously reduce flame propagation speed and heat release rate. This review provides a historical overview of decomposition behavior and flame-retardant strategies, including gaseous phase flame retardant, condensed phase flame retardant, and surface flame-retardant treatment, for flexible polyurethane foam. Additionally, the flame-retardant mechanisms and shortages of these strategies are discussed. The sustainable development of flame retardant flexible polyurethane foam is prospected from the perspective of structural modification and surface treatment of polyurethane.