An efficient field-to-line coupling method in the time-domain is developed based on the waveform relaxation (WR) techniques for evaluating the electromagnetic(EM) transient response of multiconductor transmission lines (MTLs) excited by an electromagnetic pulse(EMP). Firstly, the incident EMP electric fields on the lines are calculated as equivalent distributed sources introduced into the MTLs equations. Then, the telegraph’s equations of lossless transmission lines are decoupled by applying the WR techniques and different types of equivalent current sources at the terminal of MTLs are calculated using the iterative convolution and analytical method separately. Finally, the equivalent circuit is established and the transient currents/voltages induced on the lines are obtained by using the circuit simulation software PSCAD. The proposed time-domain method has the advantages of accuracy and high efficiency compared with the method based on finite-difference time-domain (FDTD) via two numerical examples.