Abstract: The reasons for corrosion failure of an oil pipeline in Changqing oilfield were investigated comprehensively through chemical composition analysis, metallographic examination, mechanical property testing, corrosion morphology observation and corrosion product analysis. The results show that under-scale corrosion and bacterial corrosion were the direct causes of corrosion failure for the pipeline. Anti-corrosion measures of improving the fouling tendency of water, adding scale inhibitor and fungicide at regular intervals are proposed.