In this paper, the causes of the corrosion of the fourth stage outlet heat exchanger of cracking gas compressor in the 1.0 Mt/a ethylene plant at PetroChina Dushanzi Petrochemical Company are analyzed. The reason is that the acid substances in gas condensate water corrode the carbon steel equipment. By taking some measures including adding corrosion inhibitor, the corrosion was eliminated and the operation cycle of the heat exchanger was prolonged.