<p>High-voltage electrical pulse (HVEP) technology for rock breaking is characterized by its cost-effectiveness and high efficiency. Clarifying the propagation behavior of the plasma channel in heterogeneous rocks and revealing the rock-breaking mechanism under HVEP are crucial for engineering practice and promoting the application of the technology. A polycrystalline rock model was developed, and the finite difference method (FDM) and random propagation model were employed to solve the internal electric field and plasma channel, respectively. Furthermore, the influence of rock heterogeneity on the plasma channel was also analyzed. Thermo-mechanical coupling HVEP rock-breaking simulations based on the plasma channel were performed to investigate the evolution of the rock stress field and to elucidate the underlying HVEP rock-breaking processes. The results demonstrate that variations in the dielectric constants of rock crystals significantly affect the electric field distribution, causing the plasma channel to preferentially propagate through crystals with higher dielectric constants. The injection of substantial electrical energy causes thermal expansion of the plasma channel, generating a shock wave that fractures the surrounding rock under compressive stress and forms a pulverized zone. As the shock wave attenuates into a stress wave, the stress state on both sides of the plasma channel transitions from compressive to tensile, inducing intercrystalline bond fractures and forming a radial crack zone. The random distribution of rock crystals limits the potential for increasing plasma channel complexity or length through crystal size reduction. However, decreasing crystal size increases the extent of the pulverized zone and enhances rock-breaking efficacy.</p><p><b>Highlights</b></p><p><UnorderedList Mark="Bullet"> <ItemContent> <p>Simulated electrical pulse rock breaking by finite difference and thermo-mechanical theory.</p> </ItemContent> <ItemContent> <p>Investigated the influence of rock crystals dielectric constants on plasma channel.</p> </ItemContent> <ItemContent> <p>Analyzed stress field evolution in rock under electrical pulses.</p> </ItemContent> <ItemContent> <p>Electrical pulse rock breaking is effective for fine-grained rocks.</p> </ItemContent> </UnorderedList></p>