Abstract: High voltage pulse provides a new rock breaking technology with great application prospect. In order to study the fracture characteristics of rock breakdown by high voltage pulses, and clarify the relationship between breakdown field strength and physical and mechanical parameters,electric breakdown experiments on different lithological rocks were conducted. The microscopic fracture mechanisms of rocks after breakdown were analyzed with the aid of a scanning electron microscopy,and the rupture patterns of different lithological rocks at just breakdown were compared. Besides,the influence of physical and mechanical parameters on the breakdown field strength of rocks was studied. The results of microscopic analysis show that: the region near the plasma channel shows high-temperature burning characteristics with smooth grain surface and holes;The crack region presents intergranular and transgranular fractures under shock waves;The transition area shows the joint action of high temperature and shock waves. In addition,there is little correlation between the breakdown field strength and the density, wave velocity,and elastic modulus. However,a good quantitative relationship can be established between the breakdown field strength and the compressive and tensile strengths of rocks,which increases exponentially with the increase of these two parameters.