As an important part of the guyed device of cable stayed tower, guyed rod plays a key role of preventing transmission tower from tilting and toppling. In this paper, the corroded guyed rod of 500kV transmission tower was investigated by means of macro-morphology inspection, chemical composition analysis, scanning electron micrograph analysis, microstructure analysis and energy spectrum analysis. The result showed that high content of corrosive sulfate in the soil near the leg of transmission tower was the main cause of corrosion of the guyed rod.