Under the action of high temperature plasma arc， high voltage electric pulse will produce thermal stress which can exceed the strength limit of rock， and break rocks， in particular hard rocks with obvious performance. This paper introduces the rock breaking mechanism of electric pulse. Based on the experimental data of Selfrag high-voltage electric pulse rock breaking， a simulation model of the needle electrode structure is established by using COMSOL Multiphysics simulation software. The influence of voltage， mineral composition and porosity on the distribution of electric field intensity in rock is studied. The results show that the distribution of electric field intensity is different with different applied voltage； the electric field distorts at the boundary of different mineral components， and the greater the change of relative permittivity of different mineral components， the more obvious the distortion is. Rock breaking with high voltage pulse occurs preferentially at the interface of different mineral components， and rock can be decomposed into various minerals depending on its composition. The presence of pores in the rock distorts the electric field around it； and the larger the porosity is， the easier electric breakdown the rock is.The research conclusion can provide reference for the selection of rock breaking parameters of drilling by high voltage electric pulse.