Abstract: In the anti-pollution flashover work of the state grid system, it is impossible to measure the creepage distance of electrical equipment online currently. In view of this situation, we developed an on-line measurement system of creepage distance for high voltage insulator based on binocular stereo vision, proposed a method of using a conical off-axis mirror to produce the linear structured light. We discussed the feasibility of two ways to solve the interference problem of strong sunlight, one way used narrowband filters to enhance the contrast ratio of laser line in images, while the other way processed the images with adaptive threshold segmentation and feature point extraction by combining the maximum interclass variance method with the grayscale gravity method. After calibrating the system, the measurement accuracy for the creepage distance of high voltage insulators was tested. Experimental results show that the maximum relative error is 1.45% and the average relative error is 0.69%. It has been successfully applied to the on-line measurement of the creepage distance of various insulators in 110 kV substations.