Abstract: Spot and pit corrosion was found on the surface of the sucker rod in an oil well. The causes of corrosion on sucker rod were analyzed by means of chemical composition analysis, metallographic examination, scanning electron microscope analysis, energy spectrum analysis and ion spectrum analysis. The results show that the high content dissolved oxygen and hydrogen sulfide in produced fluid of the well led to oxygen corrosion and hydrogen sulfide corrosion of sucker rod. The higher content of chloride ion accelerated corrosion reaction.