The invention discloses a transmission line inspection system based on a multi-rotor unmanned aircraft, which comprises the multi-rotor unmanned aircraft and a ground support system, wherein the multi-rotor unmanned aircraft comprises an aircraft body, an airborne flight control system, an airborne task system and an airborne power supply for supplying power to all the electronic devices; the aircraft body comprises a body, an undercarriage fixedly connected below the body, and a plurality of rotor components which are symmetrically distributed on the periphery of the body; the airborne flight control system comprises a flight navigation and control part, a transmission line anti-collision warning and control part, and an airborne end used for remotely controlling a telemetry data chain; the airborne task system comprises a damping nacelle, an image acquiring device arranged on the damping nacelle, and the airborne end for a wireless image transmission chain; and the ground support system comprises a ground end for remotely controlling the telemetry data chain, a flight monitoring system, the ground end for a wireless image transmission chain, and an image monitoring system. The transmission line inspection system has a reasonable structure, is easily realized, and has high engineering application value.