<p>Deep rock masses exist in complex geological environments characterized by concurrent water erosion and dynamic disturbances. This study investigates the dynamic response and failure characteristics of saturated red sandstone under coupled dynamic and hydro-mechanical loading through Split Hopkinson Pressure Bar (SHPB) experiments. Results demonstrate that the dynamic behavior is governed by cumulative impact load, hydrostatic confining pressure, and seepage pressure. Specifically, dynamic compressive strength increases with cumulative impact load and confining pressure, but decreases with rising seepage pressure. The energy dissipation rate exhibits non-monotonic behavior, initially increasing then decreasing with seepage pressure, while showing consistent decline with confining pressure. Fractal dimension analysis of fragmented specimens reveals that seepage pressure promotes rock fracturing while confining pressure restricts crack development. The classical pore-fracture model was enhanced through the incorporation of hydrostatic confining pressure, seepage pressure, and external impact loading. Monte Carlo simulations were employed to conduct stochastic modeling, confirming correlations among pore water pressure, confining pressure, pore radius, and fracture behavior in red sandstone, thereby validating experimental findings. Additionally, this research quantified crack propagation rates under varying confining and seepage pressures, while scanning electron microscopy analysis provided insights into the fundamental mechanisms controlling fracture evolution in red sandstone.</p>