Abstract: 760℃ high temperature low cycle fatigue tests were carried out on a new nickel-based single crystal superalloy at different strain amplitudes (0.7%-1.2%). The effect of strain amplitude on low cycle fatigue behavior of the alloy was discussed, and the fatigue plastic deformation characteristics and fatigue fracture mechanism were analyzed. The results show that low cycle lifetime decreased with increasing strain amplitude, and the degree of cyclic softening was significantly reduced. At the strain amplitudes of 0.7% and 0.8%, the plane slip of dislocation in the matrix channel perpendicular to the stress axis and the formation of dislocation slip band were the main modes of fatigue deformation; the fatigue cracks initiated at the shrinkage cavity inside the alloy; the fracture morphology was mainly characterized by fatigue cleavage step and tearing edge, and the fracture mechanism was cleavage fracture. At the strain amplitudes of 1.0% and 1.2%, the main characteristic of alloy deformation was the occurrence of dislocation shearing γ' particle and lamination; the cracks initiated at the stress concentrated slip band or micropore on the alloy surface, and the cracks propagated along the orientation 〈110〉 on 111 slip plane; the fracture morphology was mainly characterized by sawtooth steps and river pattern, and the fracture mechanism was cleavage fracture.