Composite heat storage system and method

The invention provides a composite heat storage system and an operation method, and the system comprises a heat storage module which is arranged in a heat storage tank and comprises a plurality of heat storage assemblies arranged in the vertical direction; the multiple heat storage assemblies divide the heat storage tank body into multiple heat storage areas, and the heat storage areas communicate with one another. The heat storage assembly comprises a phase change material layer and a plate storage assembly arranged below the phase change material layer. Heat exchange flow entering any heat storage area penetrates through the phase change material layer, exchanges heat with the phase change material layer and then falls onto the storage plate assembly, and when the liquid level of the heat exchange flow on the storage plate assembly reaches a set value, the heat exchange flow enters the downstream heat storage area. The heat exchange flow and the phase change material are jointly used as a heat storage mediu