Abstract: Accurate prediction of the drying time of undulating pipeline can ensure the complete drying of residual water in the low-lying sections of pipeline and prevent the water content of natural gas from exceeding the specified standard after the pipeline is put into operation. Herein, a drying time prediction model of undulating natural gas pipeline with dry air was established. Meanwhile, the geometric relationship model between the amount of liquid accumulated at the low-lying areas and the surface area was introduced, which could accurately describe the changes of residual water and surface area at low-lying areas with drying time. Besides, the accuracy of the continuous purging and plugging process was verified by laboratory experiments respectively. Moreover, the drying process was simulated with a large-diameter undulating natural gas pipeline on the site of a bid project.The results show that the dew point of the dry air should not be lower than －40 ℃ and the flow velocity should not be higher than 6 m/s when drying the undulating pipeline. The uniform water film is dried from front to back, and the residual water at the low-lying sections of the back end of pipeline is dried last. The relevant research which improves the prediction accuracy of the drying time of the undulating natural gas pipeline, could provide guidance for the design of drying scheme and the drying process of the undulating natural gas pipeline.