<p>This study investigated the effects of different CO₂ concentrations (0%, 20%, 50%, 80%, and 100%) on the decomposition behavior and kinetic mechanisms of magnesite by adjusting the CO₂ concentration in the intake zone of the TG furnace and employing a non-isothermal thermogravimetric analysis method. The thermodynamic parameters and reaction mechanism functions were analyzed using the Flynn–Wall–Ozawa equation and the Coats-Redfern equation. The results indicated that as the heating rate increased, the thermogravimetric (TG) curve shifted toward higher temperatures. Under the same heating rate, an increase in CO₂ concentration significantly inhibited the decomposition of magnesite. Additionally, the initial decomposition temperature, the temperature corresponding to the optimal production rate, and the activation energy all increased with the rise in CO₂ concentration. The evolution of the dominant mechanism was influenced by CO₂ concentration through changes in diffusion resistance and surface reaction steps. At low CO₂ concentrations (&lt; 50%), the decomposition followed a nucleation and growth model, whereas at high concentrations (&gt; 80%), it transitioned to a three-dimensional diffusion model. In industrial calcination, the calcination temperature can be optimized based on CO₂ concentration; however, it is essential to balance the thermodynamic driving force and the risk of the reverse reaction. After calcination, CO₂ should be rapidly removed to prevent the recarbonation of MgO. This study reveals the synergistic regulatory mechanism of CO₂ concentration on the decomposition kinetics and thermodynamics of magnesite, providing a theoretical foundation for optimizing the calcination process and equipment design.</p>