The invention discloses a double-fluidized-bed reactor for endothermic reactions and a method for supplying heat for endothermic reactions. The double-fluidized-bed reactor comprises: a bed body of a fluidized bed for endothermic reactions, which is closed and in which a first fluidized bed layer consisting of particles of catalyst for endothermic reactions or reactant particles, is arranged, wherein the bottom of the bed body is provided with a first gas distributor which is connected with a gas source of the first gas to supply the first gas to the first fluidized bed layer; and a bed body of a fluidized bed for supplying heat, which is closed and in which a second fluidized bed layer consisting of hot carrier particles is arranged, wherein the bottom of the bed body a second gas distributor which is connected with a gas source of a second gas for supplying the second gas to the second fluidized bed layer. The bed body of the fluidized bed for endothermic reactions and the bed body of the fluidized bed for supplying heat are embedded together. The double-fluidized-bed reactor for endothermic reactions, which is disclosed by the embodiment of the invention has the advantages of safety, stability, high heat conductivity and the like and is particularly suitable for supplying heat to medium/high temperature endothermic reactions at a temperature of above 400 DEG C.