Abstract: In the transient electromagnetic detection in mine, the results of the detection are affected by the roadway space, which is not conducive to the interpretation of the results of detection. The 3D finite element method was employed in the study to simulate the impact characteristics of roadway by establishing geological model and the distributions of transient electromagnetic field when there exists roadway or not, and then, the distribution of contour of the magnetic field intensity at different time such as 10 μs and 0.1 ms was drawn. The results showed that the spread of magnetic field in high resistance area was slower than that in low resistance area, changes of the length of roadway had great impact on the distributions of the magnetic field along its length, and changes of the height of roadway affected the distributions of the magnetic field along its height. The roadway space had great impact on the distribution of magnetic field in the early time and small impact in the late time, which provided theoretical basis for the interpretation of the results of the detection.