The invention provides an unmanned aerial vehicle system for patrolling power transmission lines, and relates to the field of power transmission. The unmanned aerial vehicle system for the patrolling power transmission lines is provided with a positioning unit, a central processor and a direction control unit, so that an unmanned aerial vehicle can fly along a positioning route automatically, a camera control unit may trigger a camera body to take photos when a third trigger signal is received within predetermined time after a second trigger signal is received, and the second trigger signal and the third trigger signal both are generated after interactive verification of a first control module on the unmanned aerial vehicle and a second control module on a power transmission cable, so that the unmanned aerial vehicle system can ensure that the unmanned aerial vehicle can take the photos in a reasonable position, and the quality of the photos can be improved.