The hidden water-bearing structures near the roadway tunnelling face are very likely to cause water seepage accidents in coal mines. Currently, transient electromagnetic (EM) technology has become an important method to detect water damage in advance of roadway excavation. In this paper, the time-domain finite element algorithm based on unstructured tetrahedron grids is used to accurately simulate the geological body in front of the roadway excavation face and analyze its response. The authors detect the distance between the roadway excavation face and the low-resistivity water-bearing body, the resistivity difference between the low-resistivity body and surrounding rock, and the influence of the size of the low-resistivity body on the transient EM response. Furthermore, the common types of low-resistivity bodies in the roadway drivage process are used for modeling to analyze the attenuation of the detected EM response when there are low-resistivity bodies in front of the roadway. The research in this paper can help effectively detecting the water-bearing low-resistivity body in front of the roadway drivage and lay a foundation for reducing the risk of water seepage accidents.