<p>Electrical breakdown is an important prerequisite for electrical fragmentation in high-voltage electrical pulse rock breaking. Currently, research on the electrical breakdown process of rocks is focused mainly on numerical simulation. Research on the variations in the microstructure, mechanical properties, and discharge characteristics of rocks during electrical breakdown is lacking. In this study, cyclic discharge breakdown tests were done on sandstone, and the breakdown voltage and current during the breakdown were analyzed. The evolution of plasma channels inside the rocks was observed using X-ray computer scanning, and the variations in internal pore properties were quantitatively analyzed. In addition, the uniaxial tensile strength (UTS) of sandstone after various discharge breakdown times was tested. The results showed that rocks’ breakdown voltage and current fluctuated during the discharge process, but the breakdown voltage of the first discharge was the highest. During the breakdown process, the plasma channels in the rock tended to become complete with increasing the number of discharges. The pulsed discharge significantly changed the pore structure parameters of the rock. After 5, 10, 15, and 20 discharges, the porosity of the rock increased by 68.4%, 79.4%, 105.3%, and 194.7%, respectively, compared to the original rock sample, and the equivalent pore diameter and the number of large-diameter pores increased with the increase in the number of discharges. Discharge breakdown significantly reduced the UTS of rocks, but the tensile strength reduction rate was fastest after the first 5 discharges. This study reveals the discharge characteristics and dynamic variations in the physical and mechanical properties of rocks during the electric breakdown process, and the results contribute to the understanding of the electrical breakdown process of rocks and its electric&#xa0;response properties. </p>