Abstract: The extraction of deep coal resources faces a geological environment with the coupling of high water pressure and high stress. The study of mechanical behavior and fracture characteristics of the fractured rock mass under hydraulic-mechanical coupling is of great significance to reveal the instability and fracture law of deep rock mass. In this paper, a single cracked limestone specimen is made by prefabricating a fissure in the middle of a limestone standard cylindrical specimen. The MTS815 rock mechanics test system and PCI-2 acoustic emission monitor are used to perform conventional triaxial compressive tests on single cracked limestone specimens under different confining and water pressures, and the acoustic emission monitoring during the fracture process, respectively. The inclination angles of the prefabricated crack is set to 15°, 45° and 75°, respectively, and the confining pressure is set to 10, 15, 20 and 25 MPa, respectively, and the water pressure is set to 0, 2, 4, 6, and 8 MPa, respectively. The results show that the stress-strain curve of a single cracked limestone under hydraulic-mechanical coupling presents a unique bimodal behavior of high front and low back or low front and high back, moreover, the stiffness of bearing structure decreases obviously after the first peak point. The crack initiation stress, dilatancy stress and peak stress of single cracked limestone all decrease obviously with the increase of water pressure, but increase significantly with an increase in confining pressure. Under the same water pressure and confining pressure, the above three stress levels with the crack inclination angle α=75° are the highest, followed by with α=15° and those with α=45° are the lowest. The crack inclination angle and water pressure significantly affect the change law of acoustic emission signal during the rock fracture process of single cracked limestone. With the increase of the crack inclination angle, the ringing count in the crack initiation and stable growth phase becomes more and more sparse. Compared with the acoustic emission characteristics under high water pressure, the acoustic emission signal is stronger under the action of low water pressure. Based on the experimental results, the compression-shear fracture criterion of single cracked limestone under hydraulic-mechanical coupling action is established. The relationship between compression-shear parameter and crack inclination angle is clarified. It is found that there is a correlation between the fracture mode and |KⅡ/KⅠ|, that is, |KⅡ/KⅠ| increases with the increase of crack inclination angle, and the rock crack subjected to combined shear and compression mode tends to shear fracture.