Abstract: As to No. 35 Valve Chamber in the 2nd Sebei-Xi'ning-Lanzhou Second-line Gas Pipeline, the 1st and 2nd of Sebei-Xi'ning-Lanzhou Gas Pipelines are connected by in-line stoppling installation technology. In-line installation in welding, tapping, plugging, pipe cutting and welding connection in gas pipeline are extremely risky, thus a safety operation measures play a decisive role in successful plugging work. This paper mainly describes measures and methods to control over the plugging safety of 1st Sebei-Xi'ning-Lanzhou Gas Pipeline, and emphasizes that controlling the contents of oxygen/flammable gas in pipe units and protecting the safety of cut pipes and valves welding with mounting insulating capsule and temporary venting device are two key links to ensure the safety of in-line tapping and plugging in gas pipelines.