The relevance of the dissolution behavior of the primary γ′ phase and abnormal grain growth in UDIMET 720LI (U720LI) alloy was studied under various heat treatment conditions and through corresponding simulation based on the classical dynamic model using MATLAB^TM. The results indicated that the dissolution kinetics and volume fraction of the dissolved primary γ′ phase increased by increasing the dissolution temperature. Additionally, an increase temperature promoted abnormal grain growth. Fine and coarse grains randomly mixed during the temperature range of 1155°C to 1170°C. The dissolution mechanism was rationalized, with the elastic splitting of the primary γ′ phase involved in the early stage of the dissolution process. The dissolution process of the primary γ′ phase was dominated by the diffusion mechanism in the latter stages. The dissolution-sensitive temperature range which should be avoid to inhibit the abnormal grain growth was given. Simulation results were consistent with the experimental data and thus the classical dynamic model was further used to investigate the influence of Al and Ti content on the dissolution behavior of the primary γ′ phase. With an increase in Al and Ti content, the full dissolution time decreased, whereas volume fraction of the primary γ′ phase increased. Volume fraction of the primary γ′ phase was more affected by variation of Al content than Ti content. In terms of the impact on the full dissolution time of the primary γ′ phase, there was no obvious difference between same variation of Al content and Ti content. Trends in the changes of the dissolution-sensitive temperature range under various Al and Ti contents were also given in this paper.