The embodiment of the invention relates to the electric power inspection technical field, and discloses a power transmission line detection method and device; the method comprises the following steps: carrying out frame difference operation between two adjacent frame images of a collected visible light video sequence so as to obtain a difference image, and binarizing same to obtain a binary difference image; using a preset threshold edge detection algorithm to carry out edge detection for the binary difference image so as to obtain an edge binary difference image; carrying out Hough conversion so as to detect linear sections; carrying out cycle iterations and screening merging for detected linear sections according to the transmission line parallel characteristics until the obtained target linear section number is smaller than a preset value, and marking and displaying same; calculating the central position of a target zone, and sending the central position to a hang cabin so as to adjust the posture of the hang cabin. The method and device can effectively improve the power transmission line detection efficiency and accuracy, thus reducing work load of inspection personnel.