High-voltage electric pulse (HVEP) rock fragmentation has demonstrated substantial potential for sustainable fracturing of hard rocks owing to its energy efficiency. The transient nature and highly disruptive characteristics of its physical fracturing process render experimental investigation of the underlying rock-breaking mechanisms challenging. However, existing numerical studies lack comprehensive models that precisely link electrical breakdown phenomena with mechanical disintegration processes. This study combines COMSOL electrical breakdown simulations with four-dimension lattice spring model (4D-LSM) mechanical analysis to establish a coupled HVEP rock fragmentation model. The core concept of the model construction is to import the temperature field of the plasma channel obtained from the electrical breakdown into the mechanical solver to realize the precise connection between the two stages. The validated numerical model elucidates the full process of HVEP-induced fragmentation under varying electrical parameters. Furthermore, the effects of confining pressure and mineral grain size on fragmentation behavior have been investigated. Finally, parametric simulations across 25 electrical parameter combinations demonstrate the critical role of electrode spacing optimization in achieving energy-efficient rock fragmentation. These findings provide a predictive tool for designing efficient HVEP systems in deep resource extraction and mineral processing engineering.