The invention discloses an online power transmission tower monitoring method and system of the power system. The monitoring method comprises the steps of data collection, data transmission, data display and analysis and early warning. The monitoring system comprises an onsite data collector, a data transmission module, a database, a data display module and an analysis and early warning module, wherein the onsite data collector synchronously collect four parameters including the wind speed and the wind direction of the wind-field environment of a power transmission tower as well as the vibration acceleration of the power transmission tower and the rod member strain of the power transmission tower, the data transmission module transmits received data to the data display module, the data display module displays the received data via a display interface, and transmits the received data to the analysis and early warning module, and the analysis and early warning compares the wind speed and the wind direction of the wind field environment, the vibration acceleration of the power transmission tower and the rod member strain of the power transmission tower with preset alarm values in the analysis and early warning module, emits alarm signals when the alarm values are exceeded, and thus, prevents the tower from falling off and prevents wires from being broken.