Hydraulic fracturing in low-permeability coal seams faces significant challenges, including poor controllability of fracture propagation and difficulty in forming complex fracture networks. Existing studies lack a systematic understanding of fracture evolution under full-cycle dynamic loading, limiting their applicability to field operations. To address this, a large-scale true triaxial physical simulation system combined with real-time acoustic emission (AE) monitoring was employed to investigate hydraulic fracturing under dynamic conditions, including stepwise pressurization and pump shut-in/re-initiation. Fracture evolution was quantitatively characterized through AE analysis and source localization. Results show that during stepwise pressurization, AE spectra exhibit a broad distribution, indicating distributed microcrack nucleation that provides preconditioning damage for subsequent fracture growth. During the fracture propagation stage, AE activity intensifies, with cumulative energy reaching 2900 mV·ms, and tensile failure dominates. Fractures preferentially propagate along the maximum principal stress direction, forming branched, tree-like structures. During pump shut-in and re-initiation, AE activity decreases and the frequency range narrows; however, newly formed fractures are concentrated within azimuth ranges of 240°–255° and 315°–345°, indicating both reactivation of dormant fractures and the formation of new propagation paths. These findings demonstrate that stress redistribution during shut-in and re-initiation governs fracture reactivation, including initiation along original and non-original paths as well as borehole-induced deviation. This mechanism plays a key role in controlling fracture propagation and enhancing fracture network complexity. The study provides new insights into fracture evolution under dynamic loading and offers experimental support for optimizing controllable hydraulic fracturing in low-permeability coal seams.