In the detection of urban bedrock surfaces, due to the severe urban traffic and electromagnetic interference, direct current sounding is often used as the main geophysical method. The two-dimensional electrical sounding profile arranges electrodes along the survey line, collects the apparent resistivity data and performs two-dimensional inversion, and uses the obtained two-dimensional resistivity cross-sectional image in the direction of the profile to infer the location and attitude of the geological body. However, due to the complicated actual situation, it is not suitable for the two-dimensional inversion conditions (infinitely extending and orthogonal to the survey line), and the two-dimensional inversion will produce large errors. In view of such a situation, three-dimensional inversion of multi-section two-dimensional electric sounding data of the survey area can be used to obtain three-dimensional resistivity stereo images of the survey area, and the spatial form of geological body distribution can be inferred. In a geological survey of a city in Shandong Province, an electrical sounding network with a distance of 50m and a line spacing of 100m was set up to collect two-dimensional symmetrical quadrupole sounding data. After establishing a three-dimensional inversion data format for the two-dimensional electrode arrangement in the survey area, a three-dimensional resistivity inversion was performed to obtain a three-dimensional resistivity image of the survey area. The inferred bedrock surface is basically the same as the drilling verification.