Abstract: Taking the tie-in practice in reconstruction and expansion of Jingxi Natural Gas Transmission Pipeline for an example, the paper describes the three tie-in techniques, that is, tie-in operation in shut down micro—positive pressure with gas, shut down and gas displacement without gas and on—line stoppling, and Drovides operation steps of these tie-in techniques.Through comparison and analysis, the paper emphasizes relative problems to be focused on when these tie-in techniques are field utilized and considers that the tie-in techniaues to be field used should be rationally determined based on efficiency, safety and economy in pipeline welding in allusion to the objective, time, welding position of pipe and gas consumption of downstream users.