The paper investigated the influence of sub-solvus heat treatment processes on the γ" phase microstructure of a novel third-generation nickel-based powder superalloy FGH4113A(WZ-A3). The temperature, soaking time, cooling rate of sub-solvus heat treatment, and the effects of super-solvus + sub-solvus, sub-solvus + sub-solvus on γ" phase were mainly explored. The results indicate that: the volume fraction of γ" phase is inversely proportional to the sub-solvus heat treatment temperature; the tendency of γ" phase dissolve back intoγ phase is inversely proportional to the size, and the quantity is inversely proportional to the soaking time; the size of grain boundary γ" phase increases with the increase of soaking time; the overall volume fraction of γ" phase does not change significantly with the increase of soaking time; a fast cooling rate can re-precipitate an intergranular fine unimodal γ" phase structure; a slower cooling rate can re-precipitate intergranular multimodal γ" phase structure; the size of the reprecipitated γ" phase is inversely proportional to the cooling rate; the microstructure after super-solvus + sub-solvus heat treatment is mainly affected by the temperature and cooling rate of the sub-solvus heat treatment, the lower the temperature, the more rectangular γ" phases are in the grain; the small size spherical γ" phase will be coarsened into a rectangle shape at high temperature, which is affected by the absolute value of the mismatch degree of the γ/γ" phase; the γ" phase microstructure of sub-solvus + sub-solvus heat treatment is greatly affected by temperature.