One of the most widely used geophysical surveying techniques in the urban environment is the electrical resistivity tomography (ERT) method. However, traditional ERT can only utilize regular grid and equidistant electrode layouts. Furthermore, all electrodes must be connected by long cables, and the existence of obstacles in urban environments makes it challenging to implement such layouts. We, therefore, present an optimized 3D ERT survey design consisting of arbitrarily distributed electrodes. We use the dipole-dipole array as the data acquisition unit. Each unit is independent and can be randomly distributed and adjusted in length. The unit can be used as a current or potential electrode as required. In this way, the limitations of grids and cables can be eliminated. Arbitrary distribution does not mean doing whatever you want. Must follow the basic principles of the geoelectric method. Based on this, we have formulated a set of reasonable procedures in the survey design, including the ‘main-subunit’ and the ‘effective measurement circle’, which make the surveying system run more quickly and accurately. We select a complex urban area with partial prior information as the field sample to verify our survey design. This approach can effectively avoid the disadvantages of the traditional ERT method and obtain correct and effective results in a complex urban environment.