During the remaining ammonia treatment process in gas refining workshop in Hanbao Coking Plant, the unstable index of ammonia wastewater, substandard ammonia nitrogen and pH，and high pressure and flood inside ammonia still tower were caused by the serious scaling in the tray and the inner wall in ammonia still tower influncing the gas-liquid transfer. Trough analysis， that is found that the scaling in ammonia still is mainly caused by the leakage of heat exchange equipment, and the scaling after the reaction of the mixing of circulating water and residual ammonia water into the ammonia tower with alkali. By regularly testing the basicity of the residual ammonia water, termly testing leakage of the ventilator, and reducing unnecessary water into residual ammonia water system, the scaling can be effectively prevented.