<p>This paper investigates the gas adsorption and gas expansion effects on crack propagation in coal, specifically addressing adsorbed-gas-induced erosion and mechanical strength weakening. Industrial CT scanning technology was used to measure crack initiation and propagation under the effect of non-adsorptive and adsorptive gases. Based on energy conservation principles, a critical fracture stress model serving as a criterion of coal crack propagation was developed, taking into account the coupled effects of gas adsorption and gas pressure. The experimental results indicated that, in the presence of non-adsorptive gas, crack volume and surface area increase at decreasing rates with rising pore gas pressure, while crack propagation is governed primarily by stress concentration and coal matrix shrinkage. Under adsorptive gas conditions, crack initiation and propagation increase in significance with adsorption time. Crack propagation usually persists for a measurable duration after gas adsorption reaches equilibrium before cessation. Besides, crack propagation in coal is mainly controlled by stress concentration, with additional contributions from coal matrix shrinkage, erosion effect, and mechanical deterioration induced by gas adsorption. In addition, the proposed critical fracture stress model gives the criterion of crack propagation in coal under the influence of pore gases. The theoretical analysis results illustrate that crack propagation occurs more easily under adsorptive gas conditions than under non-adsorptive gases, in agreement with the experimental results. These findings are significant for understanding coal or rock damage due to gas adsorption, providing theoretical support for the safe production of coal mines and the efficient extraction of coal measure gas resources.</p>