This paper investigates a rock slope with height of 100 m. It is an invalidated mine slope. This paper studies the validity and some geological interpreting keys in applying the Electromagnetic Wave Tomography to investigating engineering geological conditions. As a result, the Electromagnetic Wave Tomography is able to investigate faults, karst caves and fissure zones, structure type of rock mass and zones in the slope. Furthermore, the change characteristics of rock electromagnetic absorption coefficient are valid to illustrate integrity zoning of slope rock mass.