Abstract: In order to realize the fine detection of hydrogeological conditions by natural source single-component magnetotelluric technology, the problems of magnetotelluric signal acquisition and processing were systematically analyzed, and study was conducted for the response characteristics of underground water-rich area on magnetotelluric wave. Besides, water-richness index model was established according to the magnetotelluric sounding theory and analytic hierarchy process. Moreover, the corresponding relationship between waveform and lithology was fitted based on a large amount of experimental data, and the information on physical properties, such as the dielectric constant, elastic brittleness, density and porosity was extracted from the fractal dimension of waveform. Then, these data were assigned and normalized according to the principle favorable for water enrichment in rock strata, and further incorporated into the water-richness index model for multi-dimensional coupling calculation, thus obtaining the water-richness index value of the corresponding depth. The water-richness index contains a wealth of information on physical properties of rock strata, enhances the response amplitude of magnetotelluric wave in water-rich area, and thereby reduces the influence of change in intensity of natural field source on signal acquisition and recognition. According to the water-richness index model, double-layer array-sweep type parallel plate capacitive sensor and a magnetotelluric water detector were designed using the modern computer and communication technology, and the data processing program was developed accordingly, with the resolution of detection depth up to 0.1 m, thus capable of automatically identifying the weak signal from the deep places in the complex electromagnetic signals, and further realizing the acquisition of signal from the time-varying field source and calculating the relatively stable water-richness index. As shown by the field tests, the instrument could clearly distinguish the aquifers and water-impermeable layers, identify the water-rich areas and the tiny water-conducting channels. Generally, this technology has broad application prospects in water hazard prevention in mine, restoration and treatment of abandoned and old mined areas, grouting for water plugging, and detection of deep hydrogeological conditions.