Abstract: Underground coal gasification coupled with carbon dioxide sequestration provides a new way for the coal industry to achieve the goal of “carbon peak” and “carbon neutrality”. However, the damage of mechanical properties of burnt coal under the disturbance of supercritical carbon dioxide storage may cause the instability of isolated coal pillars, which is easy to induce the risk of carbon dioxide leakage and even cause engineering failure. In view of the lack of research on the influence of supercritical carbon dioxide on the mechanical properties of burnt coal, this paper takes long flame coal as the object and uses the self-made supercritical carbon dioxide saturation pressurization device to carry out the supercritical carbon dioxide immersion mechanical test of burnt long flame coal. The results show that: ① With the increase of temperature and supercritical carbon dioxide soaking time, the uniaxial compressive strength of burnt coal samples decreases, and the temperature has a greater influence on the uniaxial compressive strength of burnt coal samples. ② The soaking time and temperature of supercritical carbon dioxide reduce the elastic modulus of burnt coal samples, and the two are negatively correlated with the elastic modulus. The elastic modulus of burnt coal samples is more sensitive to temperature. ③ The tensile strength of burnt coal samples decreases with the increase of temperature and supercritical CO₂ soaking time, and the tensile strength of burnt coal samples changes more violently under the action of temperature. Combined with the mechanical test data, the relationship function between temperature, soaking time and compressive strength, elastic modulus and tensile strength of burnt coal samples was established. Finally, the weakening mechanism of burnt long-flame coal under supercritical carbon dioxide immersion was investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques.