The influence of different aging time at 750 ℃ on microstructure and mechanical properties of GH3625 alloy tube were investigated by means of OM, SEM, EDS, Universal Testing Machine and other means in this work. The results show that the MC, M6C, M23C6, ?? and ? phase are mainly precipitated in the GH3625 alloy at 750 ℃ for 1000 h. The grain growth in the aging process of GH3625 alloy is closely related to the phase transition behavior at the grain boundary and the solute drag of Nb atoms. Due to the transformation of different types of the phase at the grain boundaries, the grain boundaries width of the GH3625 alloy with increases initially and then decreases during the long-term heat preservation at 750 ℃. Before and after aging, the change of tensile strength of the alloy is not obvious, and the yield strength of alloy shows a trend of increasing continuously. However, the elongation of the alloy has lost by 62.55%, and the fracture mode changes from ductile fracture to brittle fracture.