Abstract: In the process of natural gas dehydration in a light hydrocarbon station of Northwest Oilfield Branch of Sinopec, molecular sieve three-tower process was adopted. During the initial stage of cold blowing, the exit temperature increased and the regeneration rate was faster. For this reason, after eliminated the equipment failure, sulfite was detected in the waste water sample from regenerated gas water separator, and combined with the results of XRF element content detection of gas sample, the essential reason of molecular sieve failure and temperature rise was that the oxygen content in the feed gas of the station was too high, which caused a series of chemical reactions among iron, oxygen and hydrogen sulfide in the drying tower and released heat. Based on above reasons, corresponding measures were taken to break the environmental conditions required for chemical reactions, consequently resuming the normal production. The operation experience of the unit could provide reference for the design and normal operation of similar units.