Abstract: Time-frequency analysis is a powerful tool of signal processing,which has been used successfully in non-stationary signals recently.This paper uses joint time-frequency analysis (JTFA) for processing transient electromagnetic (TEM) field signals that have diffuse feature in geophysical exploration.First, the transient electromagnetic response on the layered earth excited by a step pulse is simulated using digital filtering and Gaver-Stehfest; and then their time-frequency characteristics are investigated with Gabor expansion.The sequences of the earth are distinguished successfully,which provides a new interpreting method for TEM prospecting.