This paper presents a running and obstacle-navigation control principle for an inspection robot, and describes the development of control system based on a distributed expert system (DES) and electromagnetic shielding of control system. The inspection robot can run on the overhead ground wires and navigate obstacles (counterweights, clamps and towers) autonomously, and inspect the damage of 500KV extra-high voltage power transmission line equipment (towers, power transmission lines, insulators). The field experiments of running on a real 500KV power transmission line show the robot control system has possessed main functions for inspection tasks.