The invention provides an OPGW-based lightning strike flash discrimination method for a transmission line. The method comprises the following steps of step 1, collecting a lightning strike signal induced in an OPGW fiber when the transmission line is subjected to a lightning strike; step 2, performing FFT transform on the lightning strike signal having a magnitude greater than a threshold V1, anddrawing a spectrogram according to the spectral features obtained by the FFT transform; step 3, filtering the spectrogram to extract a spectral contour map; step 4, performing peak detection on the extracted spectral contour curve, sorting the corresponding frequency points according to the peak value in order from largest to smallest, and selecting the frequency corresponding to the first N peakpoints as the feature direction; and step 5, counting the value of the statistically extracted feature vector in the low frequency band as a criterion to determine whether it is greater than the set threshold F, and determining to be a lightning strike if so. The method of full-line monitoring solves the problem that the lightning strike flash monitoring distance is too short and the equipment installation is complicated, and provides a powerful basis for the development of line operation and maintenance work.