Based on finite-element numerical modeling, the authors studied the feasibility of applying the resistivity method to monitoring underground geological variations. A time-lapse subsurface monitoring method based on geoelectrical observations is proposed in this paper. The numerical modeling result using 2D resistivity forward and inversion program shows that the relative variation of resistivity can serve as a good indicator for resistivity changes both regionally and locally. High-precision and large quantities of data observations of earth resistivity constitute the foundation of time-lapse subsurface monitoring. With the well-performed 2D or 3D resistivity modeling and inversion, this technique makes geo-electrical survey a useful time-lapse monitoring subsurface method.