The leakage of underground sewage pipes may seriously affect the soil and the environment of groundwater. In this paper, an in-situ automatic monitoring device on basis of multi-electrode resistivity method was developed for the leakage of underground sewage pipelines, and it was validated by a simulated experiment in laboratory that the feasibility of the new device is feasible for real-time monitoring the leakage of underground sewage pipelines at many different groundwater levels. The experimental results indicated that small leakage of sewage pipelines could be rapidly detected by the developed monitoring device when the pipeline was located in the vadose zone. The leakage could also be monitored in a prompt manner when the pipeline was located near the groundwater level, and the extent of pollutant leakage could be speculated with the gradient change in resistivity of the soil layer above the pipeline. When the pipeline was located below the groundwater level, the device could only monitor the leakage if it reached a certain concentration to produce notable changes in resistivity, because of the rapid mixing and diffusion of the pollutant in groundwater. The device set up in this paper was found capable of real-time automatic monitoring the leakage of underground sewage pipelines buried in different depths and groundwater levels.