Safe and reliable communication technologies are the key to transmission line monitoring system. Currently, most of system use public network to communicate, condition monitoring data are difficult to transmit to the master station when signal is weak or no. To solve this problem, this paper proposes converged communication mode, that is public network and optical fiber converged. Based on the optical fiber converged communication, we design the transmission line monitoring system, including local converged communication and remote converged communication, then apply it in Qingtong canyon which is proved that the communication method is safe and reliable. The research of this paper can improve the communication quality of transmission line on line monitoring system and has a good application prospect.