The invention discloses a device and a method for judging on-off state and fault diagnosis of a high-voltage disconnector, Firstly, the video images of high voltage disconnector on-off state are captured by video camera, and a group of high voltage disconnector on-off switch is recognized by the method of HOG and SVM based on the direction gradient histogram, and the original video images are closed. Then Canny algorithm and Hough transform are used to obtain the straight line shape of the outer contour of the high pressure arm. Then, it is judged whether the image to be detected contains a specific type of high-voltage disconnector, and the switching state of the high-voltage disconnector is judged according to the magnitude relationship between the included angle of the outer contour ofthe high-voltage arm and the switch-on position judging angle N2 and the switch-on position judging angle N1. As the invention does not need to accurately model the movement of the high-voltage isolate switch, the invention is not limited to a specific type of the isolating switch, and has wide applicability; Target tracking ability is strong, stable and reliable, anti-interference ability is outstanding, can widely adapt to all kinds of field environment.