Abstract: The image extraction device was designed and manufactured to measure the surface tension of high-temperature melt based on the principle of pendant-drop method. The measuring temperature range can reach 20 ℃ to 1000 ℃. The extracted figures can be processed and the fitting calculation of surface tension can be conducted through canny arithmetic and Cyclic Coordinate Method in Matlab. The measurement accuracy is improved under the working condition of high temperature by analyzing and adjusting background light, filtering, temperature compensation and correction as well as pixel to obtain the measurement system of surface tension with a theoretical error of 0.714%. The variation of the surface tension for quaternary mixed bromide molten salt at high temperature is measured at different temperatures. The deviation ratio is lower than 1.6% when it is compared with the data measured by other scholars,which indicates that the measurement system has good credibility and is suitable for measuring the surface tension of heat transfer and storage medium in molten state.