The heating process before deformation has significant influence on the hot workability of superalloys. In this paper, the evolution behaviors of γ′ characteristic and grain structure with the heating temperature and holding time in hard-deformed superalloy U720Li were studied by isothermal heating experiments, which can provide theoretical guidance for improving its hot working performance. The results show that the area fraction and size of primary γ′ decrease with the increase of heating temperature and holding time. The dissolution of fine secondary γ′ is easier than the coarse primary γ′. The former can be completely dissolved after holding at 1100 ℃ for 30 min, while the latter can be completely dissolved after holding at 1180 ℃ for 30 min. The continuous dissolution of primary γ′ weakens its pinning effect on grain boundaries, causing the average grain size to gradually increase with the increase of heating temperature and holding time. Moreover, as the temperature increases to 1180 ℃ (higher than γ′ dissolution temperature), the grains undergo abnormal growth in a short space of time, forming a mixed grain structure. Finally, according to the grain growth behaviors under different heating conditions, a grain growth kinetic model for U720Li alloy has been established.