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Traditional rotary drilling technology generally has problems such as low rate of penetration (ROP) and high drilling costs. Electric pulse drilling (EPD) is a new drilling technology, which has the advantages of high rock-breaking efficiency and low energy consumption. To study the influence of pore characteristics in rock on partial electric breakdown (PEB) of EPD, this article takes pore in rock as the research object. First, this article analyzes the influence of pore shape and pore azimuth angle on the EPD process theoretically when the pore contains nonconductive media (such as conductivity water, air, and oil). Then, this article establishes a 2-D rock electrostatic field model with a nonconductive fluid medium in pore by COMSOL. The intensity of the electric field in the pore under the electrostatic field is taken as an evaluation index. This article analyzes the influence of the azimuth angle of the pore, the composition difference of pore fluid medium, and the relative dielectric constant of rock pore on electric field strength in pore during electric pulse rock breaking. The results indicate that the rock-breaking efficiency of the electric pulse is affected by the shape of the pore, the azimuth of the pore, and the composition of the pore fluid medium. With the increase in the azimuth angle, the greater the electric flux of the electric field in the rock with respect to the pore, the stronger and locally concentrated the electric field strength inside the pore, and the easier the rock is to have PEB failure. The electric field strength inside the rock will be distorted at the interface of different media, so the PEB failure inside the rock tends to occur at the boundary between the pore and the rock or at the weak partial dielectric strength. The research results can further deepen the research on the mechanism of electric pulse rock breaking, help better understand the pore characteristics and the mechanism of pore fluid medium on electric pulse rock breaking, and provide certain theoretical guidance and technical support for the development of EPD technology.