In this paper, we design a kind of transmission line inspection hybrid robot with a novel mechanical structure, taking the advantages of climbing robots and unmanned aerial vehicle(UAV). The hybrid robot has amphibious functions of on-wire crawling and flight. When encountering obstacles, the hybrid robot takes off directly to fly over them and it runs on the ground wire by rolling on wheels in the absence of obstacles. And then we verify its on-wire-balance by mechanical analysis. In order to achieve a tradeoff between the selection of the lightweight material and operational reliability of the robot, the finite element static structure simulation and dynamic simulation are carried out for important parts of the robot. In addition, a ROS-based robot control system has been designed and a multi-mode switching control strategy has been proposed.