Abstract: The walls of ground gathering pipelines in a gas condensate field were reduced seriously for corrosion only operation for five months. Corrosion morphologies observation, product analysis, flow velocity field calculation, simulation experiment were carried out to analyze the reasons of corrosion. The results showed that the corner of T-branch pipe and weld were corroded seriously because of CO2 corrosion and flow erosion, the main reasons was erosion corrosion caused by excessive flow velocity of fluid and unreasonable pipeline structure design, and the corrosion products were mainly composed of FeCO3.