The corrosion mechanism of the S135 drill pipes was investigated through observation of the corrosion morphology and analysis of the corrosion products by scanning electronic microscope (SEM),energy dispersive spectrum (EDS) and X-ray diffraction (XRD).The results show that the localized corrosion on the outer surface of the drill pipes was caused by oxygen corrosion due to the action of retained slurry.Cl- contained in slurry accelerated the corrosion and promoted the development of corrosion pits.Suggestions for mitigating or preventing such corrosion of the drill pipes are proposed based on the research results. The corrosion mechanism of the S135 drill pipes was investigated through the observation of the corrosion morphology and analysis of the corrosion products by scanning electronic microscope (SEM), energy dispersive spectrum (EDS) and X-ray diffraction (XRD). The results show that the localized corrosion on the outer surface of the drill pipes was caused by oxygen corrosion due to the action of retained slurry. Cl-contained in slurry accelerated the corrosion and promoted the development of corrosion pits. Suggestion for mitigating or preventing such corrosion of the drill pipes are proposed based on the research results.