The invention discloses an ammonia nitrogen wastewater treatment method and an ammonia nitrogen wastewater treatment system for a wet dust collection blast furnace gas system. The method realizes ammonia nitrogen wastewater treatment by six steps of detection of water quality conditions; lime softening; settling and separating; air stripping; blowoff, sewage discharge and decyanation treatment ofblast furnace gas. The system comprises a circumferential seam scrubbing tower, wherein a blast furnace gas inlet pipe is arranged at the top of the circumferential seam scrubbing tower; a scrubbing water return port and a scrubbing water inlet are formed in the side wall of the circumferential seam scrubbing tower from top to bottom; the side wall of the circumferential seam scrubbing tower is provided with a gas outlet; a gas utilizing system is connected to the gas outlet; a return water elevated flow slot, a settling pond, a hot water pool, a cooling tower and a cold water pool are sequentially connected to the scrubbing water return port through a pipeline; the cold water pool is connected with the scrubbing water inlet through a circular water supply pipe. According to the ammonia nitrogen wastewater treatment method and the ammonia nitrogen wastewater treatment system disclosed by the invention, the wastewater amount is reduced by using an evaporative cooling principle, and no water treatment structure or increase of energy consumption for water treatment is needed; the ammonia nitrogen wastewater treatment method and the ammonia nitrogen wastewater treatment system have thecharacteristics of less investment, low cost, reliable operation and the like.