Series of models are designed to test the influences of some parameters such as resistivity of overburden layer, basement and transmitter-receiver layouts, to a given 3D conductive anomaly in the layered earth model by transient electromagnetic (TEM) method, which is often used in engineering exploration. The forward modeling procedure used is formulated with volume integral equation based on tensor Green's function. The response of electromagnetic components are first calculated in frequency domain and then transformed to time domain by digital filtering. Through a series of modeling, it shows that the transient response of both e x and V z components are larger if the overburden layer and basement are resistive. The models also illustrate that S-s layouts are not sensitive to the variation of basement resistivity and it is more suitable for surveying shallow target.