The invention discloses a water medium type flue gas heat exchanger device. The water medium type flue gas heat exchanger device comprises a condensed water pipeline led from a seventh low-pressure heater outlet and a raw flue gas cooler, a purified flue gas heater and a booster pump which are sequentially connected; condensed water flows into the raw flue gas cooler through a valve and the pipeline from the seventh low-pressure heater outlet to absorb heat to lower the temperature of flue gas, flows into the purified flue gas heater through the pipeline to release heat to increase the temperature of purified flue gas and then flows back to a sixth low-pressure heater outlet after being boosted by the booster pump; the water medium type flue gas heat exchanger device further comprises a high-temperature condensed water pipeline of a fifth low-pressure heater outlet and a heat supplementing pump; high-temperature condensed water of the fifth low-pressure heater outlet is poured into the condensed water pipeline between the raw flue gas cooler and the purified flue gas heater after being boosted by the heat supplementing pump; the high-temperature condensed water and the condensed water flowing through an outlet of the raw flue gas cooler are mixed to increase the temperature of the condensed water entering the purified flue gas heater, and then it is guaranteed that the temperature of the purified flue gas heater exceeds 80 DEG C.