Based on linear circuit dynamic response， the analysis of the components of transient zero-mode network excitation source is presented. The full transient response of zero-mode current under that source is also analyzed. Based on the group comparison of the zero-mode transient current mandatory components a transient fault line selection method is proposed. The method conducts frequency analysis using the matrix pencil algorithm and then obtains the frequency components which have the most obvious transient characteristics to select the fault line. This method doesnt need digital filter and can reflect the real composition of the fault transient signals. This method has also high noise immunity and fast computing speed. Moreover， this method only uses the current to select fault line， so it has high reliability. ATP simulation results show that the proposed method is effective and reliable.