Abstract: In an open-pit coal mine in Hulun Buir of Inner Mongolia, the main mining coal seams are buried in depths ranging from 39m to 90m. Before coal mine integration, predatory mining has left many mined areas with unknown geological data, and the existence of mined-out areas has brought huge safety hazards to open-pit mining stripping. In order to find out the specific location and connectivity of the underground goaf, the authors used the cross-hole electromagnetic wave CT method to probe into the inside of the goaf in detail, and obtained a lot of real and reliable geophysical data. The analytical result shows that relatively complete rock formation electromagnetic wave absorption coefficient is in the range of 0.44~0.51Nper/m, and no water-filled goaf electromagnetic wave absorption coefficient is in the range of 0.29~0.40 Nper/m. According to the difference of electromagnetic wave absorption coefficient between goaf and surrounding rocks, the authors drew the morphological interpretation map of the goaf, and the results are basically consistent with the drilling data.