The invention discloses an extraction method for extracting the discharge ultraviolet imaging quantization parameters of a gray scale-based electrical device. The method comprises the steps of 1, preprocessing an ultraviolet image: firstly, selecting a valid image, specifically: 1) extracting an original ultraviolet image of each frame out of an original ultraviolet video through the image processing software; 2) subjecting the above original ultraviolet image to grey level transformation; 3) conducting the two-value transformation; 4) conducting the mathematical morphological filtering; 5) filtering out interference light spots; 2, calculating the equivalent spot area through weighing grayscale coefficients, specifically: 1) selecting a valid image ; 2) conducting the gray-scale treatment; 3) calculating the equivalent spot area. According to the invention, the description of a discharge region is realized based on light spots with gray values. Therefore, the problem in the prior art that the strength of the discharge capacity in the discharge region cannot be described can be solved. Moreover, the discharge strength and the discharge position of electrical device can be described more accurately.