The invention relates to the technical field of high voltage electric device detection, and in particular relates to a high voltage composite insulator fault detection method based on ultraviolet imaging. According to the invention, an ultraviolet imaging instrument is used to quantify discharge intensity; a discharge parameter at a critical flashover moment and an ultraviolet characteristic parameter are corresponding, so as to acquire the state diagnosis criterion of a composite insulator before flashover based on ultraviolet imaging; the corresponding relationship among the discharge plasma parameter, the discharge ultraviolet radiation intensity parameter and the electric field intensity parameter is established; ultraviolet imaging is used to detect the state diagnosis criterion of the rod-shaped suspension insulator before flashover; the concept of a plasma fitness level is introduced to acquire the state diagnosis criterion of the composite insulator before flashover based on the plasma fitness level, which is conductive to field detection; and the method is suitable for promotion and application in the technical field of high voltage electric device detection, and has positive social and economic benefits.