<p>Supercritical carbon dioxide (SC-CO₂) jet-assisted coalbed methane (CBM) well drilling technology enables dual benefits of enhanced CBM recovery and geologic carbon sequestration. The phase change-induced cryogenic thermal stress has been identified as a primary mechanism for improving coal fragmentation efficiency. Addressing the unclear knowledge regarding cryogenic flow field formation mechanisms and thermal stress evaluation during SC-CO₂ jet drilling, this study integrates numerical simulation, temperature field testing, and computed tomography (CT) to investigate the mechanism of phase change-induced low-temperature flow field of SC-CO₂ jet and to explore the damage effect of low temperature-induced thermal stress on coal and rock. The results demonstrate that the cryogenic characteristics originate from CO₂ of high latent heat of vaporization and low sensible heat. The Joule–Thomson effect during fluid expansion plays a dominant role in temperature reduction of the flow field. The extremely short phase change time and high-velocity jetting reduce the heat exchange between the flow field and the ambient medium, which together determine the generation of the low-temperature flow field. The temperature change of the carbon dioxide jet flow field is positively correlated with the ambient pressure. Under the current research conditions, the SC-CO₂ jet experienced a maximum temperature drop of about 97&#xa0;K after acceleration through the nozzle due to adiabatic expansion and phase transition. The phase change low temperature of SC-CO₂ jet can induce thermal stress in coal matrix, resulting in crack initiation, propagation, and coalescence. With decreasing jet temperature, the proportion of coal fracture area increases significantly after thermal stress, and the damage intensity in coal reservoirs increases.</p>