The paper investigated the influence of heat treatment processes on the γ" phase microstructure of a novel third-generation nickel-based powder superalloy WZ-A3. Differential thermal analysis of different heating and cooling rates, interventional cooling tests, cooling rate tests and aging heat treatment experiments were carried out in order to investigate the dissolution and precipitation behavior of γ" phase as well as its size evolution. The results indicate that: when the WZ-A3 alloy cooled from supersolvus heat treatment, the initial precipitation temperature of γ" phase is between 1148°C~1165°C, the fastest precipitation temperature is between 1028℃~1037℃; the secondary γ" phase nucleation and precipitation temperature range from 885°C to 1008°C, depending on the experimental cooling rate; a slower cooling can further obtain more secondary γ" phase precipitation; the temperature of the supersolvus heat treatment has no significant effect on the size of the γ" phase; the cooling rate after solution heat treatment is inversely proportional to the size of the γ" phase, this relationship can be expressed as a power law function y=1490.74x-0.509; the short-time aging at 800℃ has no obvious influence on the size and morphology of the secondary γ" phase; the coarsening rate of the secondary γ" phase at 800 ° C, 900 ° C and 1000 ° C are 2.153×10-28m3s-1、1.696×10-27m3s-1、and 2.331×10-26m3s-1, respectively; the activation energy of the γ" phase coarsening of the studied alloy is 278 kJ / mol.