The invention provides a boiler-discharged-wastewater treating device and method for a coke dry quenching system. The boiler-discharged-wastewater treating method includes the step that wastewater discharged from a boiler is guided into a water sealing trough of the dry quenching boiler through the boiler-discharged-wastewater treating device. The boiler-discharged-wastewater treating device is characterized by comprising a constant discharging flash vessel (1), a cooler (2) and a water tank (3), wherein the constant discharging flash vessel (1), the cooler (2) and the water tank (3) are sequentially communicated; a water inlet of the constant discharging flash vessel (1) is communicated with a wastewater discharging opening of the boiler, a water outlet of the water tank (3) is communicated with a water inlet header pipe (14) of the water sealing trough of the dry quenching boiler, and a pressurizing pump (4) is arranged between the water tank (3) and the water inlet header pipe (14) of the water sealing trough. According to the boiler-discharged-wastewater treating device and method, the wastewater discharged from the boiler is guided into the water sealing trough of the dry quenching boiler through the boiler-discharged-wastewater treating device, the wastewater discharged from the boiler is recycled, the waste, caused by direct outward discharging of the wastewater, of water resources is avoided, the water consumption of the coke dry quenching system can be effectively reduced, and the using environment of the water sealing trough can be improved.