In this paper, a method for extracting ridge in fingerprint images is proposed, then an intelligent Sobel-based algorithm for filtering fingerprint images in arbitrary direction at a filtering template at required direction is given, which can obtain satisfactory results for different quality grades of fingerprints. Experiments show that this method can estimate the direction of ridges of fingerprint in an image more exactly than most of existing methods based on discrete direction, and it is robust against those noisy fingerprints.