The invention discloses a dedusting flue for reinforcing fine particle surface steam adsorption and growing up processes, a system and a method. The dedusting flue comprises a flue gas channel, the flue gas channel is internally provided with a heat exchange tube, a heat exchange medium is circulated in the heat exchange tube, the temperature of the heat exchange medium is lower than that of flue gas in a flue gas outlet of a desulfurizing tower, flue gas in the flue gas channel and the heat exchange medium conduct heat exchange, fine particles serve as original nucleuses of water vapor generated in the condensation process, and small water drops are condensed on the surfaces of the fine particles and grow up rapidly. The dedusting flue, the system and the method have the advantages that on the basis that no large equipment is added, no huge investment is needed, existing desulfurizing and dedusting equipment is fully utilized, humidity supersaturated conditions of desulfurized flue gas are fully utilized, the fine particle surface steam adsorption and growing up processes are reinforced, fine particle capturing efficiency of a traditional wet-type electrostatic deduster is promoted, concentration of emitted fine particles in a chimney outlet is greatly reduced, and meanwhile part of water is recycled.