Abstract: The flow rate of Mohe-Daqing Oil Pipeline declined abnormally from 2 300 m3/h to 2 100 m3/h while the deployment of pumps along the pipeline was constant. As a result, the pipeline operation efficiency reduced, impacting the performance of oil transportation. In order to find out the reasons for the decline of flow rate, the unit frictional resistance losses of each pipeline section was calculated. It is shown that the frictional resistance between Mohe station and Jiagedaqi pump station increased dramatically. Then, the influential factors were comparatively analyzed, including physical properties of oil product, oil temperature and ground temperature along the pipeline, effects of drag reduction agent (DRA) addition and process change at stations. Based on field investigation, it is indicated that there are two reasons for the decline of flow rate. On the one hand, the shear effect on DRA from axial-flow one-way valve which was newly put into operation in Tahe station led to DRA failure. On the other hand, wax deposition existed in this pipeline section. After two measures were taken, i.e. process switch of Tahe station and pigging between stations, the flow rate is recovered to the normal level and the risk of inventory increasing in Mohe station is reduced. Based on the above analysis and research, a series of suggestions were proposed to deal with periodic pigging in winter, wax deposition caused by hot work of Russia oil in winter and research of flow-enhancement reform.