In recent years, many ethylene plants have encountered the problem of dew point rise at the outlet of regeneration gas heater, and the causes of dew point rise have not been found through various on-site investigations. The dew point at the outlet of the regeneration gas heater in the 600 kt/a ethane-to-ethylene plant in Tarim was also detected, and the same phenomenon was found. In order to find the root cause, heat exchanger leakage investigation, comparison of similar plants, material composition changes, process parameter verification, and material investigation were carried out to find the causes of the final dew point rise, and some suggestions were put forward for the operation.