Non-contact Measurement of circular hole, which based on machine vision is already used for industrial applications. In this paper, a novel practical method to obtain parameters of a circular hole from an image is presented. The main idea of the proposed method is that we use gradient information to find a region that contains possible centers of the circle (the hole) and use evidence-collecting process to obtain the reasonable radius. This method fits the situation that the hole object in a image is totally brighter or darker than its background. Experimental results demonstrate that our method can detect the hole with the acceptable precision and stability for practical applications.