The invention relates to a construction method for a gray-level information content histogram, comprising the following steps: acquiring the scale space expressions of an input image under different scales, and folding the input image with Gausses of different scale factors to obtain the multiscale space expression of the input image, namely a Gaussian pyramid image; acquiring the DoG pyramid multiscale expression of the input image, detecting a scale space extreme point on the basis, and storing the corresponding scale information; revising the statistical weight of each pixel, assigning 1 for the increment of the statical weight which is in a local high information area and is detected by the scale space, assigning 0 for the increment of the statical weight outside the area, and adopting a progressive scanning mode to revise the statistical weights of all the pixels in the local high information area; and respectively accumulating the statistical weights of the gray levels of the pixels, thus obtaining the measured result of the information content born by each gray level, namely the gray-level information content histogram. The invention comprehensively considers the quantity and space position distribution, so that the statistical result can better reflect the role of each gray level in describing information.