Abstract: In this paper, we studied probing depths of borehole geoelectrical resistivity observation by homogeneous half-space model and horizontally layered model with given structure parameters, and analyzed the relationship among probing depth, electrode buried depth of configuration and medium resistivity structure. The results are as follows: ① Compared with surface observation, when electrode distance is about 1 km, probing depth increases with electrode buried depth of configuration, and the increasing rate is closely related with electrode buried depth, as the increasing rate of electrode buried depth less than 100 m is much smaller than that greater than 100 m. ② When electrode buried depth of configuration is within 50 m, probing depth has a slow increase which is less than 10 m, compared with surface observation. For the same electrode buried depth, the greater electrode distance is, the smaller probing depth increases. ③ For the horizontally layered structure of homogeneous resistivity, probing depth in underlying low resistivity structure is significantly larger than that in underlying high resistivity structure under the condition of same electrode buried depth of configurations. Therefore, in order to observe the resistivity variations of deep medium, it is necessary to firstly identify the electrical structure parameters of observation area, and then determine electrode buried depth of borehole geoelectrical resistivity observation through comprehensive analyses.