To further study the problem of mine TDEM, the authors set up a model for the roadway and the abnormal body, and made numerical simulation of the transient field excited by a magnetic dipole source by using the seven node difference scheme of the diffusion equation. The result shows that the isolines of the "smoke ring" field where the conductor is located are obviously abnormal, and the effect of the conductor weakens with time. However, the abnormality where the roadway is located can last longer. The isoline section figures of the magnetic field and δH/δt are plotted on the basis of the data obtained at quite a few surveying points. The figures show that the isolines congregate towards the conductor, and the abnormality lasts longer in the isoline section figures of δH/δt.