Abstract: Based on the magnetotelluric (MT) theory, a technical law of high precision electromagnetic spectrum was illustrated. From comparative analysis of experiment, the exploring depth and the electromagnetic frequency could be regarded as a linear relation in local area, which made the stratum resistivity correspond to the exploring sounding curve. An observation system of underground coal seam resistivity using multi-channel exploring method was designed. As a sensor, the paralleled capacitor overcame the disadvantage of volume effectiveness and improved the exploring precision. The system is adopted to explore coal seam and oil-gas. In comparison with the practical drilling data, the accordance gives out a satisfied result with a figure of 80% or more.