The evolution of grain structures, γ" strengthening phases and carbides of FGH113A (WZ-A3) alloy during long-term aging treatment at 760 ℃ and 815 ℃ were studied by means of Optical Microscope (OM), Scanning Electron Microscope (SEM), and Energy Dispersive Spectrometer (EDS) and the effect of long-term aging on the tensile properties of the alloy was analyzed. The results show that the long-term aging at 760℃ and 815℃ has no significant effect on grain size and grain morphology of the alloy. After long-term aging at 760℃, the size and morphology of the γ" strengthening phases have no obvious effect, but after long-term aging at 815℃ for 440h, the γ" phases begin to grow and the morphology changes from quasi-cubic to quasi-spherical. After long-term aging at 760℃ for 2020h, the carbides have changed from dispersed granular particles to aggregated at grain boundaries. After long-term aging at 815℃ for 440h, needle-like carbides begin to precipitate in the grains. After 2020h, granular carbides are enriched at the grain boundaries and form chains, at the same time, the needle-like carbides precipitated in the grains further increased. Under the tensile tests of 704°C and 760°C, the tensile strengths of the alloy during long-term aging treatment 760°C/440h and 760°C/2020h were equivalent, but the yield strengths increased slightly after 2020h; the tensile properties of the alloy show similar discipline at 815 long-term aging. The key reasons for the better tensile strength stability of the alloy were attributed to the stable grain structures and the pinning effect of grain boundary carbides. The new nickel-based powder superalloy FGH113A exhibits excellent stability under long-term aging at 760°C and 815°C.