Abstract: The fracture mechanism of granite under the combined action of unidirectional static stress and high voltage electric pulse is systematically studied by means of experiment and numerical simulation. The self-developed experimental platform was used to carry out multiple sets of high-voltage electrical pulse fracture granite experiments under unidirectional static stress, and the rock fracture morphology and block distribution characteristics were obtained. The current waveform in the process of electric pulse breaking rock is monitored by Rogowski coil and the time history curve of plasma channel shock wave is obtained by inversion. The numerical simulation was carried out by using LS-DYNA software, and the crack propagation and damage evolution process in granite under the combined action of high voltage electric pulse and unidirectional static stress were analyzed. The results show that the static stress and boundary constraint conditions have a significant effect on the fracture of rock by high voltage electric pulse. In the absence of static stress loading, the four sides of the granite specimen are free surfaces, and the cracks show a disordered random multi-directional expansion state. In the case of unidirectional static stress loading, the loading surface of the specimen becomes a non-reflective boundary, and the other pair of planes is still a free surface, which can reflect the stress wave. Under the combined action of shock wave reflection tension and static stress on the free surface, the cracks parallel to the static load in the rock specimen are fully developed, forming a dominant propagation direction, while the cracks perpendicular to the static load direction are suppressed. With the increase of static stress, the guiding and promoting effect of static stress on parallel load cracks is enhanced, and gradually becomes dominant. The free boundary reflection tensile effect of shock wave is weakened, and the cracks converge to the middle of the specimen. In particular, there is an obvious compressive damage zone near the plasma channel, which increases with the increase of static load and consumes a large amount of shock wave energy, which is the main reason for the weakening of the free surface reflection tensile effect of the shock wave. The research results provide basic theoretical basis and technical support for the application of high-voltage electric pulse rock breaking technology in deep unidirectional principal stress engineering.