With trend of large-capacity COG purification system in coking industry,this paper discussed the advantages of large-capacity COG purification system and analyzed the operation ever since the commissioning of the COG purification system for Baosteel (Zhanjiang) Iron & Steel.The COG purification system with capacity of  1.7×105 m3/h runs successfully in Baosteel (Zhanjiang),with H2S content in COG less than 100 mg/m3throughout a year,and with all the other indexes conforming to design requirement.