Abstract: Dewatering/drying technology, which can provide a quality gas transported and prevent hydrate from forming, is a key procedure that conducts after water pressure testing. Take the dewatering/drying test as an example, which has been carried out with the dry air pigging/drying method in Sebei-Ningxia-Lanzhou Gas Transmission Pipeline, the paper introduces the process of dry air pigging/drying in a 9. 5 km water pressure testing pipe section of the line. The analysis on dewatering result and the variation of water dew point during dewatering/drying is made. The results indicate that the dry air pigging/drying method is cost-effective and the process is easy to control, suitable to apply in gas transmission pipeline.