The invention discloses a real-time online evaluation method and system for a safety state of a power transmission tower. The method comprises: acquiring wind speed, wind direction, lead wire icing thickness and temperature information by utilizing a detection instrument mounted on the power transmission tower, and transmitting the information to a sub-processor; establishing a finite element model of a line-tower coupling system of the power transmission tower by utilizing the sub-processor; loading the acquired information into the finite element model of the line-tower coupling system of the power transmission tower established in the step 2; by utilizing a calculation module in the sub-processor, obtaining an integral structure stress condition of a power transmission line according to the step 3, and performing extractive analysis on counter point displacement, a slenderness ratio, tension and bending stresses, compressed bar stability and axial force; and transmitting an extractive analysis result in the step 4 to a main processor through a wireless network by the sub-processor. According to the real-time online evaluation method and system, a pre-warning signal can be triggered when the power transmission line is in special climate or a running condition of the line is seriously abnormal by monitoring and evaluating the structural state of the power transmission tower, thereby providing basis and guidance for safety operation maintenance and management decision of the power transmission line.