Abstract: High-voltage electric pulse (HVEP)drilling technology has become a new rock-breaking method characterized with high rock-breaking efficiency and good borehole wall quality. To study the impact of rock pore characteristics on its partial electric breakdown, this paper establishes a two-dimensional numerical model of multi-physical field coupling electric breakdown with random distribution of multiple pores. Based on this, a whole process of high-voltage electric pulse plasma generation and rock breaking in porous rock is achieved by the coupling of circuit field, current field, breakdown field and temperature field. This paper mainly investigates the law of impact of pore characteristics (i.e., porosity, pore size and pore medium)and electrode spacing on partial electric breakdown of rock (i.e., formation of plasma channel in rock). The numerical research indicates that the porosity of rock has a great impact on the rock-breaking efficiency of high-voltage electric pulses. When the medium in pores is air, electric breakdown takes place in pores, and plasma channel runs through the pores. When the medium is water, there is no electric breakdown in pores, and plasma channel extends along pore surface. As the porosity increases, the rock-breaking effect of electric pulses will be gradually enhanced. As the ratio of pore media water to air decreases, the generation time of plasma channel shortens, and the rock-breaking efficiency of high-voltage electric pulses gradually increases. As the electrode spacing enlarges, the electric breakdown time of the rock gradually shortens, and the area of "electric injury" in rock decreases. In addition, a laboratory experiment on rock breaking by electric breakdown is also carried out to reproduce the process of rock breaking by high-voltage electric pulses and the morphology of plasma channels in rock, and it is found that the experimental results of electric breakdown are consistent with the simulation tests.