Analysis is made to the factors affecting the operation of COG ammonia scrubbing by H3PO4 for 7 m top-charge battery.Measures are taken by optimizing the demisting process of ammonia absorber,improving de-oiling efficiency from rich oil,restructuring heat exchanger and improving lean liquor de-sludging,etc..After the optimization,stable operation of the ammonia scrubbing system by H3PO4 can be extended from 3 months to 12 months,and the H3PO4 consumption rate can be reduced from 2.3 kg/t to 1.7 kg/t,which plays a decisive role in COG purification and stable delivery.