The invention provides a building auxiliary haze-reducing mist-spraying, cleaning and fire-fighting jet device, a water distribution branch pipe is arranged at the top of an outer wall surface of a building, a plurality of multifunctional mist-spraying jet sprayer nozzles are mounted on the water distribution branch pipe which is communicated with a water tank by a water distribution main pipe, and a pressure control water pump which can adjust the water pressure is arranged on the water distribution main pipe. According to the building auxiliary haze-reducing mist-spraying, cleaning and fire-fighting jet device, a haze monitoring device can be used for monitoring the PM 2.5 concentration value around the building, when the concentration value is larger than the set threshold value, the pressure control water pump is started, the pumped low-pressure water enters the multifunctional mist-spraying jet sprayer nozzles through one-way valves, spraying mist is formed, and the requirement for reducing the haze around the building is met; when the pressure control water pump pumps high-pressure water, the high-pressure water enters the multifunctional mist-spraying jet sprayer nozzles, jet is formed, and the fire-fighting and outer wall surface cleaning functions are met.