The invention discloses a wastewater concentrating system and method utilizing flue gas waste heat and based on liquid column evaporation. The system comprises an evaporation tower and is characterized in that the evaporation tower is arranged on one side of the gas inlet end of a desulfurization tower and communicated with the desulfurization tower; the evaporation tower is provided with a spraying area inside, the spraying area comprises a plurality of vertical liquid column spraying orifices used for spraying wastewater, flue gas enters the evaporation tower through the flue gas inlet of the evaporation tower and transfers heat and mass with the wastewater sprayed by the liquid column spraying orifices vertical to or intersecting with the flue gas, the wastewater evaporates after absorbing heat to generate steam which enters the flue gas, the flue gas flows out through the flue gas outlet of the evaporation tower and enters the desulfurization tower, the liquid column spraying orifices are connected with a wastewater storage tank, the evaporation tower is connected with the wastewater storage tank, and the evaporated wastewater enters the wastewater storage tank so as to achieve wastewater circulating concentration. The wastewater concentrating system has the advantages that flue gas waste heat is utilized on the basis that boiler efficiency loss is avoided, the problem of blocking is avoided, wastewater treatment quantity is lowered greatly, desulfurization water and water replenishing are reduced greatly, energy and water are saved, and huge economic and environmental benefits are produced.