Abstract: The economical and efficient audio magnetotelluric sounding method is used to detect the central axis of the tunnel，and then the data are processed by SSMT2000，MTsoft2D and other software. Finally，the electrical structure characteristics of the study area are analyzed by the inverted apparent resistivity profile，so as to speculate the geological structure characteristics，water-rich conditions and spatial distribution of unfavorable geological bodies. Audio magnetotelluric sounding method is sensitive to low-resis⁃ tance anomalies in high-resistance geological bodies in the study area. Low-resistance areas are mostly weak strata such as water-bearing faults or karst caves. Such unfavorable geological bodies are the main targets for research and are of great significance to the development of the project.

Key words: geologic investigation, audio magnetotelluric, electrical characteristics, fault