Abstract: China’s energy infrastructure is characterized by a coal abundance, oil scarcity, and limited natural gas. Coal resources dominate the country’s energy landscape. However, while coal gasification technology can enable the green utilization of these resources, it also generates substantial residue. Storing this residue poses environmental risks due to potential pollution and results in the wastage of valuable land. Additionally, these stored residues contain valuable elements that cannot be reused. A significant challenge in the current resource utilization processes of coal gasification slag is the mutual restriction between carbon and ash content in the slag. HSC 6.0 was used to calculate the Gibbs free energy of oxides in coal gasification fine slag from the Yulin region, considering different CO formation probabilities. The relationship between the reaction heat (Q) of coal gasification fine slag, CO formation probability (η), and oxygen content (O%) was also examined. The thermodynamic calculations suggest that the chlorination reaction of oxides in coal gasification fine slag is feasible. By adjusting the chlorine-to-oxygen ratio in conjunction with variations in η, it is possible to maintain the system’s thermal equilibrium and ensure the sustained progression of the reaction.