China Steel Chemical Corporation (CSCC) is the world's only one plant which adopted the circulation loop oil as heat transfer fluid in her production process. CSCC's plant has been long suffered from serious corrosion problems in pipeline and equipment. In this study, self-established Parr simulated corrosion test, combined with on-site operation information collected and parsed, as well as circulating oil analysis were integrated to identify the causes of corrosion. And finally by developing a way to put corrosion inhibitor into circulation oil, the corrosion rate was significantly reduced from 40 ~ 90 mpy to 0 ~ 10 mpy. As a result, the corrosion phenomenon was effectively improved.