The corrosion behavior of "Qing-Ha" oil pipeline was examined by magnetic flux leakage, the corrosion mechanism belong to the oxygen depolarization corrosion and localized corrosion process. Based on the testing of soil resistance ratio and corrosion potential, the corrosion rank of the soil was regarded as strong corrosion type. The pitting occured at some positions of welding seams for the crack and residual stress, and also some parts of pipeline under the cross and span of pipeline for the soil oxygen concentration cell. The disrepair of the outer corrosion resistant layer in addition to the stray current led to the crack failure.