Abstract: According to the fluid law of fluid pipeline and the drag reducing mechanism, it is pointed out that natural gas pipeline's drag reducing principle is to suppress the gas pulsation between the thin layer and pipe wall.It is considered that internal coating, liquid film, injecting liquid drag reducing agent into condensed liquid and making gas drag reducing agent adsorbing on internal wall are the effective drag reducing methods of natural gas pipelines.As the result shows that gas drag reducing agent is a kind of polymer(compound)with long polymer and non-polymer molecular chain.