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Study on the high cycle fatigue fracture characteristics and damage mechanism of nickel based single crystal superalloys at 850 °C. The results indicate that high cycle fatigue cracks in single crystal superalloys generally originate from defect locations on the subsurface or interior of the specimen at 850 °C. Under the condition of stress ratio R=0.05, as the fatigue load decreases, the high cycle fatigue life gradually increases. The high cycle fatigue fracture is mainly characterized by octahedral slip mechanism. At high stress and low life, the fracture exhibits single or multiple slip surface features. Some fractures originate along a vertical small plane and then propagate along the {111} slip surface; At low stress and high lifespan, the fracture surface is prone to alternate and expand along multiple slip planes after originating from subsurface or internal sources, exhibiting characteristics of multiple slip planes. Through electron backscatter diffraction analysis and transmission electron microscopy analysis, it is known that there is oxidation behavior on the surface of the high cycle fatigue fracture, and the fracture section is composed of polycrystalline layer, distortion layer, and matrix layer from the outside to the inside. Among them, the main components of the polycrystalline layer are Ni and Co oxides; The distortion layer is mainly distributed in the form of elongated or short rod-shaped Al, Ta, and W oxides; The substrate layer is a single crystal layer.