During the construction, reroute and repairing of long-distance pipeline, magnetic blow in pipeline junction is frequently occurring.Magnetic blow, which means welding arc deviation, will lead to welding defect or even welding failure, and then, seriously affect the progress of the project and the essential security of pipeline.The pipeline remanence will lead to magnetic blow, resulting in welding defect and thenseriously affect the essential security of pipeline.After the study of mechanism and hazard of residual magnetism in pipeline and the comparison of pipeline remanence index at home and abroad, a verification experiment of the China-Russian Eastern Gas Pipeline Project has been made for defining the effect of remanence on welding.The experimental results show that the welding operation can be carried out only when the magnetic field strength of the pipeline is lower than 5 mT. The test results will effectively guide the welding operation of the China-Russia Eastern Gas Pipeline.