Abstract: The stability of CO₂-sequestered coal seams may be affected by geological disturbances such as strata reactivation, and CO₂ generally exists in a supercritical state during geological sequestration. To investigate the influence of impact loading disturbances on coal seams used for CO₂ storage, dynamic compression and dynamic splitting tests were conducted on coal specimens subjected to different supercritical CO₂ (Sc-CO₂) erosion durations of 0, 2, 4, 6 d, using a high-pressure gas adsorption–desorption system and a split Hopkinson pressure bar (SHPB) testing system. In addition, scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) were employed to characterize the micro- and meso-scale structural features of the coal. The variations in dynamic strength parameters, energy evolution, and failure-crack characteristics of the coal were systematically analyzed. Meanwhile, a standard deviation standardization method was introduced to eliminate dimensional differences among different parameters and to quantitatively compare their relative variation magnitudes. The results indicate that Sc-CO₂ significantly promotes the development of micro-pores and micro-cracks in coal and preferentially damages polar or weakly polar functional groups, resulting in a reduction in oxygen-containing structures, weakened intermolecular interactions, and a tendency toward structural aromatization. Consequently, the structural strength of the coal is degraded. With increasing erosion duration, the compressive strength of the coal specimens decreases from 30.44 MPa to 14.84 MPa, while the tensile strength decreases from 5.17 MPa to 2.68 MPa. The elastic modulus and loading rate also decline to varying degrees, exhibiting a nonlinear degradation pattern characterized by rapid deterioration in the early stage and gradual attenuation in the later stage. Under both loading modes, the proportion of reflected energy gradually increases, whereas the crushing energy dissipation and energy utilization efficiency progressively decrease. After 6 d of erosion, the energy utilization efficiency under impact compression decreases to 13.90%, representing a 57.03% reduction compared with the uneroded coal specimens; under impact splitting, it decreases to 6.89%, corresponding to a 16.28% reduction. These results suggest that the energy required for coal to reach the failure threshold is reduced after Sc-CO₂ erosion. Furthermore, both the surface crack ratio and crack fractal dimension of the coal specimens increase with erosion duration. The crack propagation induced by impact failure becomes more irregular, with increased branching and a more complex fracture network. The influence of Sc-CO₂ on peak strength and strength degradation degree is more pronounced under impact splitting conditions, whereas its effects on crushing energy dissipation, energy utilization efficiency, surface crack ratio, and crack fractal dimension are stronger under impact compression conditions. This reflects the differences in energy distribution and failure mechanisms under different dynamic loading modes. The findings of this study provide theoretical guidance for the stability evaluation and protection of coal seams used for CO₂ geological sequestration.