The invention provides a defect analysis method, a defect analysis device and a defect analysis system for an electric transmission line based on image processing. The method comprises the following steps: setting a flight command of an unmanned aerial vehicle according to position information of the electric transmission line input by a user; sending the flight command to the unmanned aerial vehicle, wherein the unmanned aerial vehicle flies according to the flight command; monitoring the unmanned aerial vehicle, namely when the distance from the unmanned aerial vehicle to the electric transmission line is smaller than a set threshold value, sending a command of starting shooting to the unmanned aerial vehicle, wherein the unmanned aerial vehicle photographs the image data of the electric transmission line; in the shooting process of the unmanned aerial vehicle, sending adjusting commands to the unmanned aerial vehicle for many times so as to adjust the operating states of the unmanned aerial vehicle, wherein the unmanned aerial vehicle photographs the electric transmission line from many angles; acquiring the image data photographed by the unmanned aerial vehicle; and determining the defects of the electric transmission line according to the image data. The method, device and system provided by the invention can efficiently and accurately examine defects of the electric transmission line and solve the problems that the workload is great and the efficiency is relatively low when the electric transmission line is polled manually.