Abstract: During the reuse of underground space in mine, coal masses are subjected to multi-axial and multi-directional dynamic disturbances induced by multiple sources, such as instantaneous strata fracturing, blasting, and earthquakes, thereby increasing the likelihood of dynamic disasters. A comprehensive understanding of the mechanical response of coal under dynamic three-dimensional impact loading is critical for the safe and efficient reuse of underground spaces. A dynamic true triaxial electromagnetic Hopkinson bar system was employed to conduct synchronous dynamic true triaxial impact tests on coal specimens at strain rates of 10−100 s⁻¹ by adjusting the charging voltage, elucidating their deformation behaviors and disaster-inducing mechanisms. During impact loading, the discrepancies in arrival time and amplitude of the stress waves under triaxial and six-directional synchronous loading were maintained within 5 μs and 1%, respectively, demonstrating excellent loading consistency. The specimens reached dynamic stress equilibrium along each axis at approximately 90 μs, which was maintained for more than 70% of the impact duration, thereby satisfying the requirements for dynamic stress equilibrium. The results indicate that, as the strain rate increased, the peak dynamic stress and strain of the coal specimens increased approximately linearly. Furthermore, more cracks were observed on the specimen surfaces, and local corner failure became more evident at higher strain rates. By contrast, the elastic modulus was insensitive to the strain rate; The post-peak shape of the dynamic strain stress curves along the three principal axes exhibits a stress rebound characteristic, suggesting that the stored elastic energy in the specimen during impact loading was released, leading to partial deformation recovery. As the strain rate increased, the macroscopic compressive deformation of the coal specimens in each axial direction after impact gradually decreased and even changed to expansive deformation at high strain rates, indicating the reopening of compacted cracks after external dynamic constraints were removed. Under dynamic true triaxial synchronous impact loading with equal amplitudes, the coal specimens were subjected to an approximately balanced triaxial dynamic compressive stress environment, which suppressed crack development and propagation; consequently, no significant failure occurred within the main structure. In contrast, under dynamic true triaxial synchronous impact loading with unequal amplitudes, the changes in the intermediate principal stress promoted tensile deformation of the coal specimens along the minimum principal stress direction, thereby inducing crack shear slip and through-going failure. Compared with equal-amplitude loading, unequal-amplitude loading generated a principal stress difference that more readily promoted conditions for crack shear slip. This demonstrates that the dynamic principal stress difference state is an important mechanical factor that induces dynamic disasters. Therefore, during the reuse of underground mine spaces, particular attention should be paid to variations in three-dimensional dynamic principal stress differences caused by multidirectional disturbances, and local deviatoric stress concentration should be controlled to reduce the risk of dynamic disasters in coal masses subjected to complex dynamic disturbances.