The invention provides a broken strand detecting method and system for a transmission conductor. The broken strand detecting method comprises the steps of collecting to-be-detected images shot by a video collecting device; detecting the to-be-detected images by means of a line segment detection algorithm, generating a backup segment gather image; screening the backup segment gather images based onthe preset line length threshold value and pixel average gray value, generating lead segment gather images; conducting binarization on the lead segment gather images, generating binarized images; detecting the binarized images by means of the preset lead broken strand outline module, and determining the position of the lead broken strand in the binarized images. The invention is advantageous in that the time consumed for detecting the lead broken strand can be shortened, and the detection is easy to realize; the demand for practical engineering application is met, and the accuracy and stability of detecting the lead broken strand can be increased; the real-time detection function of the broken strand in the line-cruising monitoring can be realized.