As environmental protection has drawn increasing attention all around the world, natural gas has been increasingly used for its high efficiency, cleanliness, and low cost. However, the frictional resistance in transportation causes a large loss of energy, thereby reducing the transportation capacity. To address this problem, this work analyzes the hydraulics of natural gas pipeline transportation, the regularity of the effects of a drag reduction agent (DRA) on the pipe inner-surface roughness, the relationship between the drag reduction effect and DRA injection technology (different doses and injection methods), and the flow pattern improvement regularity of the DRA membrane acting on the near-wall region of the pipeline. Through these studies, the fundamental reason for frictional resistance has been found, and the drag reduction mechanism has also been identified. Field test shows that the application of DRA could reduce the frictional loss by 12-16.5% in the gas pipeline transportation and raise the transportation efficiency by 8-12%.