The utility model discloses a flue gas bypass evaporator suitable for treating desulfurization wastewater of a power plant. Each air inlet pipeline is communicated with an inlet in the top of the spray evaporator body; the clear water pipeline and the wastewater pipeline are communicated with an inlet of the wastewater pump; an outlet of the waste water pump communicates with one end of a water conveying pipeline; the other end of the water conveying pipeline is communicated with an atomizing nozzle in the spray evaporator body after being combined with a compressed air pipeline through a pipeline; wherein a clean water valve is arranged on the clean water pipeline; a wastewater valve is arranged on the wastewater pipeline; each air outlet pipeline is communicated with an air outlet in theside surface of the spray evaporator body; the ash hopper is communicated with the bottom outlet of the spray evaporator body, the outlet of the ash hopper is communicated with the ash silo, and theoutlet of each air outlet pipeline is communicated with the inlet of the electric precipitation system, so that the evaporator can effectively solve the problems of scaling in a flue and serious corrosion of downstream equipment and the flue, and meanwhile, zero emission of desulfurization wastewater is realized.