Abstract: Karst formations represent a common adverse geological phenomenon in engineering construction, which may cause karst water gusher, ground collapse, cave collapse, leading to severe property damage and potential casualties. Consequently, there is an urgent need to survey the spatial distribution of karst formations. Geological drilling is a common method for karst exploration; however, it is costly, inefficient, and prone to misinterpretation. Electrical resistivity tomography (ERT) has the advantages of convenient data processing, clear imaging, strong anti-interference capabilities, low cost, and has been widely applied in the detection and imaging of coal mine goafs, landslides, reservoir leakage, and karst formations. In this study, the resistivity response characteristics of karst in the coastal city are studied by the ERT method, and validated through drilling. Experimental results indicate that the bedrock surface inferred by the ERT method closely match the core samples. Karst filled with low-resistivity media such as saturated sandy soils appear as U-shaped bedrock surface anomalies in the ERT inversion results.