The purpose of this paper was to explore the thermal fatigue deformation and fracture mechanism of single crystal alloy and enrich the theory related to it. A nickel-base single crystal superalloy was employed to study OP thermo-mechanical fatigue behavior by using scanning electron microscope (SEM), transmission electron microscope (TEM) and some other research methods. The main results are summarized as follows:A mean tensile stress is observed in OP TMF. With the mechanical amplitude increasing from 0.6% to 0.9%, the fatigue life decreases, whereas the stress range and the plastic strain increase. The cyclic stress response curve of the alloy shows cyclic hardening at half cycle of low temperature while at the high temperature half cycle, the maximum compressive stress decreases during test, indicating a cyclic softening. The main mechanism for OP TMF is the formation of local slip bands in {111} planes. The interaction of creep, oxidation and fatigue damage lead to shorter life for TMF than isothermal fatigue. The fracture and propagation of slip bands is the main fracture style for OP TMF. The tensile stress is dominant factor affecting the fatigue life in the test.