The application background of Unmanned Aerial Vehicle(UAV) power inspection is introduced. A new passive positioning technology－image-based transmission pole tower positioning technology is put forward. An image-based positioning algorithm is proposed, while analyzing the source of error. The aerial camera with Position & Orientation System(POS) can draw large scale of the topographic map，and The process of drawing the topographic map is actually the target positioning process. Carrier photoelectric turret equipped with high-precision POS system and high-definition camera, is utilized in the UAV transmission line inspection to complete the target tower real-time positioning, with positioning accuracy of 5 m.