Underground engineering has always been a difficult problem in construction.Underground engineering is a hidden project.The underground geological environment is complex and variable，and the tunnel engineering is huge.If the underground geological conditions cannot be accurately detected，there is a great potential safety hazard during the construction process.In this paper，combined with the actual tunnel engineering，the numerical analysis software GprMax2.0 is used to carry out the forward analysis of the electromagnetic wave propagation characteristics of the geological radar in the cave，and the electromagnetic waveform diagram is theoretically obtained.Secondly，the geological radar test technology is used in combination with the field test.The tunnel face was advanced for geological prediction，and finally verified by actual excavation.The related cave geoelectric model was established and the relevant fluctuation characteristics of the fracture zone were obtained.