This paper analyzed the effects and abilities for using high-density Electrical Resistivity Tomography (ERT) to indentify the three-dimensional fractures networks in the different states bedrock in-situ, by the field experiments which were done in the granite. The results indicate that it is feasible to identify the fractures networks in the bedrock for which the electrical property is high-resistivity. And the resistivity around the fractures can reflect the positions of spatial distribution and the shapes of fractures very well. But the effects and abilities of recognizing the fractures networks are related to the measurements-direction.