The invention belongs to the technical field of waste gas treatment, and relates to an ammonia fog collecting and treating system for an electrolytic plant. The system comprises an electrolytic area,inter-cell air suction pipes, branch air suction pipes, a main air suction pipe, an ammonia absorbing tower, a fan, a chimney, and a laminating device; the inter-cell air suction pipes are arranged atthe positions, above the outer side walls of electrolytic cell sets on the two ends and above adjacent side walls of the adjacent electrolytic cell sets, in the electrolytic area, the inter-cell airsuction pipes, the branch air suction pipes, the main air suction pipe, then ammonia absorbing tower, the fan and the chimney are sequentially connected, the laminating device covers the cell faces ofthe electrolytic cell sets, the two sides of the laminating device are arranged above the inter-cell air absorbing pipe, and an air suction opening is formed in the side wall of the inter-cell air absorbing pipe. The system is used for effectively solving the problem that due to the too large electrolytic cell span of the electrolytic plant, waste gas collecting and treating are difficult, the ammonia fog collecting and treating efficiency is high, the effect is good, no wastes are discharged, the system is environment-friendly and energy-saving, resource use is reasonable, and the system isgood in economic benefit.