In order to solve the problem of accurate detection of old goaf water accumulation area, the single component magnetotelluric detection technology of natural source was deeply studied. Using a component of natural electromagnetic field, the physical property information of rock stratum was extracted by Fourier series decomposition, and the influence of rock stratum on electromagnetic wave was quantified. The physical property index model was established, and the main influencing factors including dielectric constant, density, elastic brittleness, porosity and cementation degree of rock stratum were normalized and calculated, which could better reflect the obvious physical property difference between old goaf and surrounding rock. According to the physical property index model, the MaxwIII lithology detector and the corresponding data processing program were developed. The instrument was used to carry out the detection experiment of the old goaf water accumulation area in Huasheng Coal Industry, which could effectively identify the fault, goaf and water accumulation area. The drilling verification showed that the detection results were accurate. The equipment was light, simple, economical and efficient, and had the dual functions of earthquake and electric method. It had wide application prospects in the fields of underground goaf area, water accumulation area detection, grouting water plugging, old goaf water pollution control and so on.