In view of the fact that tunnel advanced geological prediction cannot effectively predict the flood in front of the tunnel face, this paper proposes a new method, i.e., transient electromagnetic wave-field transform continuation and imaging, which is based on the theory of floating plate and has proved to be very effective in predicting the unfavorable geological body in front of the tunnel face. With this desirable 3-D virtual velocity continuous analysis method, the problems of velocity extraction of observed data in migration imaging can be well solved. This paper puts forward the suitable working method of transient electromagnetism for the application in tunnel. In addition, the theoretical models and application examples were analyzed and calculated, and the results obtained coincide with the actual situation, showing that this velocity analysis method is feasible and effective.