Abstract: In order to investigate the impacts of material strength, initial crack opening, initial slit length, and the axial compressive stress on the critical water pressure for hydraulic splitting of the rock masses, the cement mortar is selected as the substitute material for a rock mass, and it is subjected to hydraulic splitting tests to examine its hydraulic splitting mechanism. The experimental analysis results indicate that a positive correlation exists between the critical water pressure for the hydraulic splitting and the material strength and the axial compressive stress of the rock mass. The axial compressive stress is found to have a larger impact on the critical water pressure for the hydraulic splitting than that of the material strength. However, the critical water pressure for the hydraulic splitting has a negative correlation with both the initial crack opening and the initial slit length, with the latter being more sensitive to the critical water pressure for the hydraulic splitting than the former. When the water pressure in the rock cracks increases, the tip of the initial crack expands and allows more fissure water to infiltrate the damaged and degraded zone. Under the dual mechanical effects of fissure water, the fractures and pores in the damaged zone expand and interconnect to form macrocracks. These macrocracks are in turn subjected to similar dual mechanical effects. Eventually, the stress intensity factor at the tip exceeds the tenacity of the cracks, resulting in destabilization and destruction of the rock mass. Under the action of the double mechanics of water flow in the rock, the stress intensity factor of the crack tip exceeds the fracture toughness, and the rock mass is unstable.