The utility model relates to the technical field of chemical offgas treatment, and particularly relates to a washing system for ammonium phosphate offgas. The washing system comprises three circulating grooves and three washing chambers, wherein each level of circulating groove and each level of washing chamber are communicated through a fire current pipe and a counter current pipe, three levels of circulating washing systems are available, each level of washing can circulate separately, the first level of washing chamber, the second level of washing chamber and the third level of washing chamber are communicated through flue gas pipelines, and the first level of circulating groove, the second level of circulating groove and the third level of circulating groove are communicated through washing liquor pipelines. The flow directions of the flue gas and the washing liquor are effectively controlled, the offgas is discharged after first level of washing, second level of washing and third level of washing, the washing liquor for second level of washing and third level of washing flows back to the first level of circulating groove, when the density of ammonium phosphate in the washing liquor reaches over 1.20g/cm<3>, the ammonium phosphate is ultimately discharged into a slurry collecting groove for recycling. The washing system effectively controls the flow directions of the offgas and the washing liquor, and prevents washing liquors of all levels from being mixed.