Abstract: To investigate the failure and instability mechanism of coal-rock combinations with different interface dip angles, a series of conventional triaxial compression simulation tests under a confining pressure of 4 MPa were conducted on coal-rock combinations with dip angles of 0°, 15°, 30°, 45°, and 60° using discrete element numerical simulation software. The mechanical properties, stress evolution, crack evolution, failure patterns, and acoustic emission (AE) signals of the coal-rock combinations were systematically studied, and the failure mechanism was further explored. The results show that with the increase in dip angle, the peak strength and total number of cracks of the coal-rock combinations gradually decrease; the elastic modulus increases significantly only at a dip angle of 60°; the crack propagation direction changes with the increase in dip angle, indicating a variation in the failure mode of the coal-rock combinations. The final failure pattern gradually transforms from an “X” shape to a “V” shape with increasing dip angle, and the failure region gradually approaches the lower right of the coal body and the interface, with cracks also appearing in some parts of the rock mass. At a dip angle of 60°, the failure surface is parallel to the interface. The duration of AE signals decreases and the peak occurs earlier with increasing dip angle, suggesting that the final failure degree of the coal-rock combinations reduces but the failure time advances. With the increase in dip angle, the failure mode of the coal-rock combinations gradually changes from shear failure to interface slip failure, and the failure region shifts from the coal body to the interface. At small dip angles, the interface effect is weak, and the failure of the combinations is mainly controlled by their material properties. With the increase in dip angle, the interface effect becomes significant, and slip dislocation becomes the dominant failure mode. Under large dip angle conditions, the final failure of the coal-rock combinations is mainly attributed to the structural instability of the interface.