Abstract: GH984G alloy cold-rolled seamless tube samples were treated by solid solution at 1 050-1 200 ℃ for 10-90 min, and influence of solid solution on microstructure and hardness of the alloy was studied. The results show that the grains of the cold-rollled alloy were elongated, and second phase particles precipitated on grain boundaries and in grains. After solid solution under different conditions, the alloy had equiaxed crystal structures; the grain size increased and the quantity of the second phase decreased with the increase of temperature and the extension of holding time. The apparent activation energy of grain boundary migration of the alloy increased with the extension of holding time, and the kinetic time index increased first and then decreased with the increase of temperature. The hardness of the alloy decreased with the increase of solid solution temperature and holding time, and had the Hall-Petch relationship with the average grain size.