The utility model discloses a waste heat boiler water desulfurization device. The device comprises a flash tank, a blowdown tank, a water storage tank, a zinc oxide slurry preparation tank and a desulfurizing tower, an inlet of the flash tank is connected with a boiler water discharge pipe; an outlet of the flash tank is connected with an inlet of the blow-down tank through a first single-stage pump; an outlet of the blowdown pool is connected with an inlet of the water storage tank through a second single-stage pump; an outlet of the water storage tank is connected with an inlet of the zinc oxide slurry preparation tank through a third single-stage pump; a zinc oxide smoke dust inlet is formed in the zinc oxide slurry preparation tank; wherein an outlet of the zinc oxide slurry preparation tank is connected with the lower part of the desulfurization tower through a slurry supply pump, a smelting flue gas inlet is further formed in the lower part of the desulfurization tower, the bottom of the desulfurization tower is connected with a zinc oxide slurry spraying pipe arranged at the upper part in the desulfurization tower through a zinc oxide slurry circulating pump, an electric demister is arranged at the top of the desulfurization tower, and a chimney is arranged at the top of the electric demister. According to the utility model, the purpose of treating waste with waste can be achieved, new water and sodium hydroxide can be greatly saved, and the cost is effectively saved.