Abstract: The main reason for corrosion of oil pipelines in Qinghai oil field has been studied. High concentration of Cl^-,salts, high mineral degree are main factors to influence the corrosion of pipelines. Bacteria also assist corrosion. Localized corrosion induced by Cl^- and bacteria was accelerated.Simultaneously the pipelines also suffer from SCC induced by H2S. The pipeline steel could possibly leak by pitting or abrupt fracture by stress corrosion.