Superalloys are critical materials for hot-section components of aero-engines, which operate for extended periods in demanding environments characterized by high temperatures, corrosive media, and cyclic stresses. Their fatigue properties directly influence the service life and safety of these components. After fatigue testing of superalloy K417 at 650 ℃, the samples with shorter fatigue life were studied. In order to find out the cause for the shorter fatigue life, observation on fracture and surface trace, microstructure examination and EDS analysis on micro areas were carried out. The results show that the shorter fatigue life of some samples is because there were spots by oxidation corrosion on the surface of the samples, and fatigue cracks initiated from the spots. The surface of the samples were polluted by foreign matter consisting of the elements of Na, Cl, K and Mg, then oxidation corrosion occurred at the polluted regions under the coeffect of high temperature and stress, and finally the spots by oxidation corrosion became fatigue source under alternating load. Because high temperature components in aero-engines chronically endure the coeffect of corrosive media, high temperature and cyclic stress, the damage mechanism and behavior of superalloys under high temperature, corrosive media and cyclic stress should be paid more attention to.