Groundwater in the bedrock mountain area is mainly structural fissure water. As development of the mountain structural fissures has no direction and is easily impacted by terrain conditions, some conventional geophysical technologies have their limitations, which adversely affects the prospecting result. Based on a study of both "TM" and "TE" observation mode response characteristics by the audio magnetotelluric sounding method, the authors have found that the comparative application of two observation modes can obviously lead to know the anisotropy of strata, with the TE observation mode showing better performance in identifying the spatial distribution of structures. Through the practice application in Taihang Mountain area, the availability of the technique has been verified, thus providing supporting technology for the prospecting of structural fissure water in mountain areas.