The invention relates to an automatic insulator string identification method based on optical images. The method comprises steps that optical image acquisition, an industrial camera is mounted on a robot to acquire data of an insulator string to acquire the optical images; optical image pre-processing, the optical images with the insulator string are pre-processed to acquire an area of interests; optical image characteristic extraction, in the area of interests, a gray characteristic curve model is established, a gray periodic characteristic matrix and a gray threshold characteristic matrix are constructed, and insulator string characteristics are extracted; insulator string type identification, insulator string type identification is carried out according to the insulator string characteristics. The method is advantaged in that insulator string type identification is carried out according to the insulator string characteristics through utilizing the gray periodic characteristics and gray threshold characteristics, identification result accuracy is high, work efficiency is improved, and bases are provided for accomplishing later washing tasks of transformer station inspection robots.