The invention discloses an overhead power transmission line vibration monitoring system and an overhead power transmission line vibration monitoring method. The monitoring system comprises a laser vibration-measuring device, an iron tower controller and a remote monitoring terminal, wherein the laser vibration-measuring device is connected with the iron tower controller through a lead; the iron tower controller is connected with the remote monitoring terminal through an optical fiber composite overhead ground wire; the iron tower controller comprises a case; a power supply module, a communication module, an alarming module and a control module are arranged in the case; the control module is respectively connected with the power supply module, the communication module and the alarming module; the communication module is connected with the remote monitoring terminal through the optical fiber composite overhead ground wire. Due to the fact that the vibration condition of a power transmission line is monitored in real time by a laser vibration-measuring method, the accuracy of monitoring result is improved; due to the fact that the movement track of the lead in a vibration process is measured and recorded in a non-contact way, the overhead power transmission line vibration monitoring system is not required to be mounted on the power transmission line, the mounting difficulty is reduced, and the mounting cost is reduced.