Abstract: Aiming at the disaster of hydraulic fracturing induced by seepage-stress coupling in saturated rock masses of reservoir bank slopes and underground caverns in hydraulic and hydropower projects, based on fracture mechanics theory, this study employs the energy release rate method to investigate the Mode Ⅰ fracture propagation mechanism of water-saturated rock mass fractures under hydro-mechanical coupling effects.By comparing the stress intensity factor at fracture tips with material fracture toughness, systematic calculations are conducted to determine critical water pressures and crack initiation angles under various working conditions.The results reveal that increasing lateral pressure coefficient significantly reduces critical water pressure, rendering the rock mass more susceptible to compression-induced splitting failure.Concurrently, crack initiation angles exhibit a pronounced positive correlation with lateral pressure coefficient, while remaining essentially unaffected by fracture length.Depth effects demonstrate dual-mode characteristics: when lateral pressure coefficient is below 1, critical water pressure increases with depth and shows an initial rise followed by decline as fracture inclination angle grows.When exceeding 1, critical water pressure decreases continuously with depth while displaying non-monotonic variation (first decreasing then increasing)with fracture inclination angle, accompanied by pressure transitions from positive to negative and back to positive.Notably, the emergence of negative pressure phases drives pore water migration toward fractures, establishing a positive feedback mechanism for hydraulic fracturing that accelerates failure processes in fracture systems.