Urban main water supply pipelines are mostly buried along roads. Large pipe diameters and deep burial depths make it hard to detect their leakage in the early stage. Their leakage will severely influence urban traffic and residents' daily life. Hence, the leakage monitoring of water supply pipelines is particularly important. However, factors such as dense traffic lines, hardened road surfaces, and electromagnetic interference limit the application of the ground resistivity method and geological radars in pipeline monitoring. To make up for the shortcomings of existing monitoring methods, this study explored the cross-hole resistivity method for pipeline leakage monitoring. First of all, pipelines with and without leakage were simulated using forward modeling and inversion methods, analyzing the detection characteristics of the cross-borehole resistivity method. Then, electrode materials and burial methods were examined through experiments, solving the problems of electrode corrosion and weak electric field signals. Finally, an experimental site was set up near a water supply pipeline in Beijing, obtaining multi-phase monitoring data using the cross-borehole resistivity method. Through comparative analysis of multi-phase resistivity sections, this study analyzed the changes in pipeline leakage, delineating the leakage influence scope, which was verified by the leakage data from the waterworks. The satisfactory monitoring results suggest that the method proposed in this study can be referenced for similar pipeline leakage monitoring in cities.