The adoption of robots instead of humans to achieve lean management of overhead transmission lines is of great significance in addressing the impact of structural shortages in line operation and maintenance. Aiming at the problems of current inspection robots in terms of heavy workload,low inspection efficiency,and low intelligence,a three-arm inspection robot and a matching suspension bridge device design method were proposed,including overall design,structural design,control system,perception system,etc. The key mechanism of the robot and the suspension bridge crossing device were simulated and analyzed,which verified the rationality of the robot structure design and the feasibility of the suspension bridge crossing device. The prototype test results show that the robot only needs bridge facilities at the tension tower to achieve continuous and reliable autonomous inspections across the entire line.