Abstract: Crude oils went through buried pipelines by their original pressure to transfer stations after pumping out from wells. They were heated, dried and pressured, and then transported to oil-gas united stations for further complicated processing such as desulfuration, dehydration and oil-gas-water separation, and finally sent outside through long-distance pipelines. In consideration of the complexity of technological process and the dangerousness of transmission medium, an early-warning system of risks is required not only for the process of gathering and transportation, but also for the buried pipelines between wells and oil-gas united stations. Since crude oils are untreated until transporting to united stations, the buried pipelines between wells and united stations are easily to be corroded and crack. Therefore, a risk evaluation and preventive measure of buried outer pipelines are really needed. A case study was made in AZ1 transfer station, S area in an oilfield in northwestern China. We collected and counted all corrosion reasons for three years, and studied normal operations, operation risks and corrosion causes using Fault Tree Analysis (FTA). An early-warning system of risks and some preventive measures were provided.