Abstract: CO₂ mineralization has attracted significant attention as a permanent carbon sequestration technology. However, research on the use of coal gasification slag (CGS), a large-scale alkaline solid waste, for CO₂ mineralization is limited. This study selects coal gasification slag from the Naomaohu area in Xinjiang as the raw material and conducts experiments on CO₂ mineralization using a direct aqueous phase method. The effects of reaction temperature, initial pressure, liquid-solid ratio, reaction time, and reaction atmosphere on mineralization efficiency and CO₂ absorption rate are explored. The optimal mineralization conditions for coal gasification slag are determined, and the mechanism of direct aqueous mineralization of coal gasification slag is elucidated. The results show that the gasification slag is rich in alkaline elements such as Ca²⁺, Na⁺, and Fe³⁺, with CaO content of up to 18.89%, primarily in the form of limestone (CaCO₃) and gehlenite (Ca₂Al₂SiO₇). Increasing reaction temperature significantly improves mineralization efficiency and CO₂ absorption rate, although the rate of improvement gradually slows. Pressurization enhances mineralization efficiency but reduces CO₂ absorption rate. Under conditions of 300 ℃ and 5 MPa, the mineralization efficiency reaches 89.05%, corresponding to the CO₂ fixation of 75.86 kg CO₂/t CGS. The mineralization efficiency exhibits a trend of initial increase and subsequent decrease with an increasing liquid-solid ratio, peaking at 10 L/kg. The mineralization efficiency under simulated pure CO₂ conditions is the highest among the three reaction atmospheres tested, while the CO₂ absorption rate under simulated air combustion flue gas conditions is higher than other gases, reaching 76.39%. Considering all factors, the optimal reaction conditions for the CO₂ mineralization of coal gasification slag are determined to be a reaction temperature of 300°C, an initial pressure of 3 MPa, a liquid-solid ratio of 10 L/kg, and a reaction time of 40 minutes. The study reveals the gas-solid-liquid three-phase reaction mechanism of the CO₂ mineralization process of coal gasification slag, which essentially involves the reaction of gehlenite with CO₂ to form calcium carbonate. It further clarifies that the leaching of Ca²⁺ from gehlenite by H⁺ is the rate-controlling step of the carbonation reaction.