In order to effectively extract Brillouin frequency shift of Brillouin distributed optical fiber sensing system and reduce data processing time, an edge feature extraction method of Brillouin scattering spectral image based on second-order Laplacian edge detection operator is proposed. The Brillouin frequency shift is regarded as the edge of the scattering spectral image, and the second-order Laplacian edge detection operator is used to sharpen the Brillouin scattering spectral image, the binary image is obtained by non maximum suppression and adaptive threshold to remove the invalid edge, and the Brillouin optical time domain reflection temperature sensing system is built. The experimental results show that the method can accurately extract the frequency shift feature, and the processing time is far less than that by using curve fitting method, which are conducive to shorten the temperature measurement time of the system.