The common-mode signal transmission and suppression are attractive from the viewpoints of the channel-capacity improvement and adaptive cancellation of the unwanted radiation from the power-line. To study this transmission and suppression, a channel modeling method based on the transmission-matrix theory is proposed in this paper. And the proposed modeling accuracy is evaluated by using an LCL probe which the authors had developed. As an application example of the proposed model, the channel capacity depending on the electrical unbalance of power-line channels is approximated for the common-mode signal transmission. ? 2005 IEEE.