High temperature low-cycle fatigue tests and high temperature tensile tests were designed to study the effects of high temperature low-cycle fatigue damage on mechanical properties of FGH96 powder metallurgy superalloy. The microscopic mechanism of the change of the mechanical properties of FGH96 alloy was analyzed by observing the fractographs. Results show that the yield stress and tensile strength of FGH96 alloy show an upward trend in the early stage of damage due to the effects of dislocation motion; in the later stage of damage, the elasticity modulus and tensile strength of FGH96 alloy are continuously degraded as the internal cracks increase and expand. The change of the mechanical properties of FGH96 alloy shows a clear correlation with the stress level. The microfracture analysis shows that with the increase of the damage degree, the high temperature tensile fracture mode gradually changs from ductile to brittle, and is accelerated by high temperature oxidation.