The invention discloses a robot for inspecting quality of electric transmission lines at high altitudes. The robot comprises a front axial arm and a rear axial arm which are parallel to a lead. The adjacent ends of the axial arms are fixedly connected to a middle rotary joint. The front axial arm and the rear axial arm are fixedly connected with a front cantilever and a rear cantilever through quick-mounting mechanisms respectively. A front driving wheel and a rear driving wheel are arranged on the upper portions of the front cantilever and the rear cantilever respectively. The front driving wheel and the rear driving wheel contact with the lead through the lower side of the lead. A horizontal locking guide rail is arranged on the upper portion of each cantilever. Two locking pawls capable of moving oppositely are arranged on each locking guide rail, incline toward each other and are staggered along the movement direction. Through opposite movement of the locking pawls, the driving wheels can contact with or separate from the lead; the robot is positioned below the lead except the locking pawls, so that on-line and off-line operations of the cantilevers can be rapidly and reliably realized; manipulation and structure of the robot can be simplified; the robot can be rapid to demount and convenient to transport.