As a new non-mechanical rock breaking technology， high voltage pulse discharge rock crushing technology has a broad application prospect in hard rock drilling. In this paper， based on the analysis of the mechanism of rock crushing by high voltage pulse discharge， the COMSOL Multiphusics software is used to establish the electric-thermo-mechanical multi-physical field coupling model， and to carry out the simulation research on the breaking law of granite and sandstone under the action of voltage， electrode spacing， electrolyte and other conditions. The results show that the broken area of rock increases linearly with the increase of voltage. The increase in electrode spacing results in the decrease in the rock fragmentation area. The conductivity of liquid medium has little effect on discharge results. The broken area of rock can be increased effectively by using multi-electrode pair discharge. The results can provide reference for high voltage discharge rock crushing technology