The excitation signal type and cycle selection are important factors affecting Transient Electromagnetic Method(TEM) system detection ability. Using the time-domain finite element integration method to simulate different excitation signals, through the contrast and analysis of the transmitter coil magnetic field distribution characteristics and magnetic focusing effect in the same depth, the excitation signal types can be determined. For the detection depth and sensitivity depending on the excitation signal cycle, the minimum period of the excitation signal is determined. Taking the minimum period as the lower limit, the simulation is carried out in different cycles, and the receiving coil of the echo effect diagram and the magnetic flux change curves of equivalent depth are obtained. Comparison and analysis are conducted to determine the appropriate cycle. The conclusion is that the rectangular pulse with 500 ms is more suitable as excitation signal, and is helpful to magnetic field energy focusing and the depth of propagation. Finally, the steel plates with different thicknesses are simulated, and the relationships between the echo signal and the thickness of steel plate are analyzed. This work can provide a theoretical basis for the practical transient electromagnetic detection system.