The invention provides a blast furnace slag washing water steam white smoke elimination system and method. The system comprises a slag washing opening, a chemical feeding device, a gas-water heat exchanger, a steam white smoke eliminating comprehensive device, a mechanical draft cooling tower and a slag washing pond; the steam white smoke eliminating comprehensive device comprises an exhaust fan,a mixing area, a demister, a spraying layer, a padding layer and a water collection pond from top to bottom, the spraying layer is connected with an outlet of the mechanical draft cooling tower, the water collection pond is connected with the inlet of the mechanical draft cooling tower and the slag washing pond through bypasses, the gas-water heat exchanger is provided with a cold air inlet, a hotair outlet, a circular slag washing water inlet, and a circular slag washing water outlet, the circular slag washing water inlet is connected with the slag washing pond, the circular slag washing water outlet is connected with the slag washing opening, the cold air inlet is connected with atmosphere, and the hot air outlet is connected with the mixing area of the steam white smoke eliminating comprehensive device. Through the blast furnace slag washing water steam white smoke elimination method, the blast furnace slag washing steam can be deeply purified, emission amounts of pollutants of sulfuretted hydrogen, sulfur dioxide and the like can be reduced, and the system water consumption is reduced.