Abstract: The cross-well electromagnetic wave CT technology is based on the difference of the physical properties between the media. Different materials have different reflective and absorbing abilities to electromagnetic waves. Interwell electromagnetic wave CT technology has a good effect in detecting Karst cracks and other aspects. In this paper, using interwell electromagnetic wave CT technology to tested the underground Karst development area of Sujiatang. Through studying the difference of rock electromagnetic wave absorption coefficient in the working area. Four layers of Karst development areas of underground were divided. The correctness of the detection results was verified by comparing with the core data of boreholes. The detection results provide necessary basic data for engineering design and construction.