Abstract: Corrosion occurred in oil-water mixed transportation pipeline in Honghe oilfield. The effects of CO₂ partial pressure, water content of the pipeline fluid, Cl^- concentration, sulfate reducting bacteria (SRB) content and temperature on the corrosion rate of 20 steel for mixed transportation pipeline were studied by a self-made high-temperature and high-pressure dynamic corrosion evaluation device. And the main influencing factors were determined based on the experimental data and through the gray relation analysis. The results showed that the corrosion rate of the 20 steel increased exponentially with the increase of temperature and water content. When the CO₂ partial pressure and SRB content increased, the corrosion rate of 20 steel first increased significantly and then slowly increased in a linear trend. And the corrosion rate of 20 steel showed a linear trend with the increase of Cl^- concentration. The influence degree of corrosion factors was ranked from large to small as following: water content>temperature>Cl^- concentration>CO₂ partial pressure>SRB content, in which the water content and temperature were the two most significant influencing factors to the corrosion of the 20 steel.