Abstract: Generally, long-distance gas pipeline operated with high pressure will be not shut down unless necessary, and if the flange connected with gas truck line leaks, it will be very difficult to plug the leakage under pressure by online way. This paper analyzes different leakages dangers occurring in flanges of pipeline, establishes a simulation test system, and puts forward a technical approach to the repair of damaged flange with high-pressure clampls, stopple and composite material repair technology. In the practical application process, a cost-effective technical solution should be selected under the premise of ensuring operation safety according to different flange leakage situations, and this is the key for successful control of flange leakage of pipelines.