The invention relates to a phase change heat accumulation system for generating steam directly and a preparation method of a phase change heat accumulation agent. A phase change material is enhanced with graphite foam, and is absorbed in a porous medium of the graphite foam, so that a binary eutectic salt / graphite foam material is prepared and is used as a composite phase change material of a heat accumulation device, the composite phase change material is high in heat conduction coefficient, therefore under the same design condition, the phase change heat accumulation system provided by the invention is applied to systems of a focusing type solar thermal power generation system, an industrial waste heat recovery system and the like, and has the characteristics of high heat transfer efficiency, small volume, low cost and the like. In addition, the phase change heat accumulation system for generating steam directly can flexibly adopt a parallel connection or serial connection mode according to the temperature of high-temperature waste heat steam and the requirement of a steam user; and during serial connection, the binary eutectic salt / graphite foam composite phase change material can be combined in a cascaded manner according to a melting point, thus the efficiency of an energy accumulation system is increased, and the energy can be greatly accumulated.