The invention discloses a desulfurization waste water concentration decrement device. The device comprises a pre-treatment unit and a first electrodialyzer; the first electrodialyzer comprises a firstcompartment, a second compartment, a third compartment and a fourth compartment, wherein the pre-treatment unit is communicated with the second compartment, and a nanofiltration system is installed at a water outlet end of the first compartment; a first concentrated water pipeline and a first fresh water pipeline are arranged at a water outlet end of the nanofiltration system, and the first freshwater pipeline is communicated with a water inlet end of the fourth compartment; a salt adding unit is arranged at the water inlet end of the fourth compartment; a water outlet end of the fourth compartment is communicated with a water inlet end of the first compartment through a pipeline; the desulfurization waste water concentration decrement device further comprises a pure water supply unit, and the pure water supply unit is communicated with water inlet pipelines of the first compartment, the third compartment and the fourth compartment through pipelines. According to the desulfurizationwaste water concentration decrement device, assemblies are little, the cost is low, and the use effect is good.