High-voltage electrical pulse (HVEP) rock-breaking technology is extensively utilized due to its advantages of high energy density, controllable fragmentation zones, and tunable energy output. However, the intricate pore structures within rock masses can significantly affect their electrical and mechanical properties, thereby influencing HVEP performance. To elucidate the mechanisms by which pore structure influences rock-breaking outcomes, this study integrates the finite difference method (FDM) and stochastic propagation model to simulate the electrical breakdown paths. Furthermore, the numerical simulations of HVEP-induced rock fragmentation are conducted using the discrete element method (DEM) based on thermo-mechanical coupling theory. The results demonstrate that the pore structure strongly impacts both the complexity of the breakdown path and the resulting fragmentation efficiency. In non-porous rocks, breakdown paths are primarily governed by rock heterogeneity, resulting in a complex branching structure. In contrast, in porous rocks, breakdown paths are guided by pore spaces, which reduces path complexity. Notably, under constant porosity, pore diameter exerts a nonlinear influence on path complexity. Smaller pore diameters, which correspond to a higher pore density, significantly enhance path complexity. Conversely, as pore diameter increases and the number of pores decreases, path complexity exhibits a ‘rebound’ as the governing mechanism shifts back to inherent rock heterogeneity. Moreover, the pore structure induces stress concentration, promoting fracture initiation and propagation, which enhances rock-breaking performance. Although rocks with small pores exhibit higher breakdown-path complexity, their fragmentation efficiency is lower than that of large-pore rocks. This finding highlights the dominant role of pore-induced stress field alterations. This study provides valuable theoretical guidance for the application of HVEP rock-breaking technology in porous rock fragmentation.