Abstract: The most commonly used sag adjustment method in transmission lines is to manually adjust the position of the connection hole of the DB-type adjusting plate, which has the characteristics of high safety risk and low operation efficiency. In this paper, by studying the size and relative position of the connecting holes of the DB-type adjusting plate, under the conditions of satisfying the hole margin, material strength and thickness, a geometric design method of the adjusting plate quadrant is established, and the design is convenient for manual adjustment, saving hardware materials, and safe and reliable operation. The adjustment hole connection method is determined by mathematical derivation, and the size of the adjusting plate is uniquely determined, and the optimal solution in line with the design specification is obtained. At the same time, in order to achieve the goal of safety and efficiency, according to the characteristics of the adjusting plate, the design concept of integrated protection was creatively proposed, and the adjusting plate with its own backup protection was invented to realize the adjustment of the sag with its own backup protection and fast and efficient. The line length is adjusted and tested by the power industry power line equipment quality inspection and testing center to meet the industry use standards.