An image definition evaluation function method based on strong edge detection comprises the following steps of step 1, setting an edge detection operator, namely an eight-direction Sobel operator; andstep 2, setting of a judgment image definition evaluation function, wherein the intensity mean value of the strong edge pixels is adopted, and the adopted eight-direction template is the converted template shown in the step 1. The method has the advantages that the eight-direction template is adopted, gray differences in different directions are considered, and the edge extraction effect is enhanced; by considering the spatial position relation between the positive direction of the current point and surrounding points, weights which cannot be too large in difference should be given, and introduction of noise is avoided; the calculation formula of the edge intensity, namely the gradient value of each pixel point in the image, adopts a normal form 1 calculation method, so that the time required by square resquaring operation is greatly saved, and the extraction of the edge points of the image is facilitated.