The invention provides an expansion type heat exchanger based on mixed heat exchange. The expansion type heat exchanger comprises an expansion section, a water supply section, a partition, a water supplement port, an inlet, an outlet, a direct mixing heat exchanger, a water distribution mechanism, a filler, an annular weir plate, an automatic exhaust valve and a liquid level sensor. The heat exchanger and an expansion water tank are organically combined, the structure is reasonable and compact, the utilization rate of equipment is increased, the manufacturing cost is lowered, and the occupiedspace is reduced. By the adoption of the expansion type heat exchanger, the mixed cold and hot compensation heat exchange of cold and hot water is realized, the environmental heat exchange load is reduced, and meanwhile water supplement, constant pressure and elimination of system gas or over-filled water are realized. The expansion type heat exchanger is flexible and convenient to use, compact instructure and environmentally-friendly, saves water, saves energy and is widely applicable to cold and hot water supply occasions with different temperature regions and different heat loads.