The effect of high temperature annealing on microstructure evolution of Ni-24Fe-14Cr-8Mo alloy was investigated through Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Rockwell Hardness Testing Machine. Three kinds of grain growth patterns were found at different annealing temperatures due to carbides precipitation and dissolution. After a combination of high temperature annealing and aging treatment, the hardness versus time curves performed a parabolic pattern. The highest hardness was achieved under 1070°C/60 minutes treatment, and the desirable annealing time should be 60 minutes to 90 minutes.