Abstract: The phenomenon of gas blockage, which is very easy to occur during commissioning of hilly pipeline, will affectthe safety of pipeline. In order to ensure that a newly-built pipeline can be put into service successfully, a new methodwas proposed to predict the pressure drop. In the method, the pipeline in the process of liquid-gas displacement is dividedinto three sections, including the gas accumulation section, the bubble section and the turning section, and the calculationmethod of pressure drop is given for each section separately. In the case study, the proposed method was applied to acrude oil pipeline in China during commissioning to predict the pressure drop along the pipeline. The results show that thecalculations are in good agreement with the field data, which can provide theoretical guidance for pressure drop predictionof similar pipeline during commissioning.