The invention discloses an on-line temperature measurement system for a strain clamp of a power transmission line and a temperature measurement device thereof. The system comprises the strain clamp, atemperature measurement sensor, a data gateway, a background server, a working host and an individual soldier control panel. The temperature measurement sensor is installed on the strain clamp in a threaded detachable connection mode, so the temperature data of the strain clamp is directly collected; and then the acquired data is transmitted to a data gateway in a 433MHz wireless data transmission mode; the data gateway transmits the data to the background server, and the background server pushes the data state information to the working host; the data gateway is provided with a Bluetooth module, and a field maintenance operator establishes a connection channel with the data gateway through Bluetooth carrying the individual soldier control panel to read temperature data. According to theinvention, through real-time temperature measurement, data transmission and automatic analysis, the time length of hidden danger discovery is reduced, the position of a defect is accurately positioned, the frequency of power failure maintenance is reduced, and the efficiency of strain clamp defect identification is improved to the maximum extent.