Thermo-Calc software was used to calculate the thermodynamics of nickel-based corrosion resistant Hastelloy G3 alloy, and the influence of composition on the precipitation of equilibrium phase was systematically studied. The precipitated phase of alloy after aging treatment was observed by the SEM and TEM. The results show that the equilibrium phases of alloy precipitation are mainly σ phase, μ phase, M6C and M23C6; the content of Cr and Mo mainly affect the precipitation of σ phase and μ phase and the initial precipitation temperature; while the content of C significantly affects the precipitation behavior of carbides M6C and M23C6; The precipitation rule of precipitates during the aging process is further studied through experiments.