The invention discloses an electrolyzing device for removing ammonia nitrogen in ammonia nitrogen wastewater. The electrolyzing device comprises an electrolytic cell, anode plates, cathode plates, ananode fixing device and a cathode fixing device, wherein at least three groups of electrode slots are sequentially formed in the electrolytic cell, and a baffle for limiting the flow direction of theelectrolyte into an S shape is arranged between each two adjacent electrode slots; and the electrode slots include anode slots and cathode slots, the anode plates are arranged in the anode slots, thecathode plates are arranged in the cathode slots and are connected with the cathode fixing device, and the anode plates are connected with the anode fixing device. The invention further discloses a method for removing ammonia nitrogen in the ammonia nitrogen wastewater by virtue of the electrolyzing device. The electrolyzing device is utilized for treating the ammonia nitrogen wastewater and has the effects that the effect is stable, the secondary pollution is avoided, the treatment efficiency is high, the structure is simple, the operation is simple, the cost is low, and ammonia nitrogen in the ammonia nitrogen wastewater treated by virtue of the electrolyzing device can be decreased to below 10mg/L.