This paper describes the data acquisition and data processing method for EH-4 electromagnetic imaging system and its detection of the deep extension of the structure. In the Juzhugou ore district, the drilling verification shows that EH-4 electromagnetic imaging can clearly distinguish the mineralized alteration structural belt and the surrounding rock, The mineralization anomaly is caused by the vein, whose resistivity is about 1500~2500Ω·m. Deposit case study shows that EH-4 continuous conductivity imaging measurement of the apparent resistivity of two-dimensional-depth profile can clearly reflect different underground geological structures of fine resistivity, and can interpret spatial distribution of mine tectonic belt and mineralization anomalies. Practice has proved that EH-4 technology is effective in the detection of deep structure extension.