Direct liquid-phase carbonation of alkaline solid waste is an effective way to fix CO2. In this paper, the reaction characteristics of direct liquid phase carbonation of carbide slag waste to fix CO2 were studied. Based on a high-pressure reactor at room temperature, the effects of liquid-solid ratio (5-20), carbonation time (0-4 h) and reaction pressure (0.1-1.0 MPa) on carbonation rate and CO2 fixation capacity of carbide slag were studied. The results show that carbide slag has good CO2 fixation ability, and the whole carbonation reaction is basically completed within 1 h. The CO2 fixation ability increases with the increase of liquid-solid ratio and reaction pressure. The CO2 fixation amount of calcium carbide slag is 9.26 mmol/g under the optimal operating condition (1 MPa, liquid-solid ratio 20) for 4 h reaction time, while the CO2 fixation amount of calcium carbide slag is only 3.58 mmol/g under the condition of 0.1 MPa and liquid-solid ratio 5. It is proved by SEM and TGA that a large amount of CaCO3 is formed after carbonation of carbide slag, and the particle size of the carbonated product is significantly reduced. Therefore, the direct liquid phase carbonation of carbide slag has better CO2 fixation ability and higher carbonation efficiency under the condition of normal temperature and pressure in the reactor. The results of this study can provide basic theoretical support for the application of calcium carbide slag accelerated mineralization to fix CO2.