In order to determine the cause of the corrosion of the heat exchange tube of the natural gas cooler of a natural gas processing plant, a Scanning Electron Microscope, an energy spectrum analyzer and an X-ray diffractometer were used to analyse the corrosion morphology, corrosion products and physical appearance of the heat exchanger tubes of the natural gas coolers. Gas chromatography was used to study the working medium of the heat exchanger tube, together with the simulation test method, the plate count method and the electrochemical method. The research results show that the corrosion of the heat exchanger tube is mainly caused by the corrosion under the scale and b y the fact thatthe corrosion protection coating is not up to standard, and the existence of crevices and bacteria further accelerated the corrosion under the scale. Therefore, during the construction of similar projects, attention should be paid to the drying and protection of the heat exchanger after the water pressure test, the cleaning during construction process and the prevention of dirt being re-introduced into the cooler while cleaning using circulating water. If the corrosion protection coatings do not meet the required standard, rather than protecting the heat exchanger tubes against corrosion, localised corrosion will accelerate instead.