Fingerprint enhancement is important for improving the accuracy of minutiae extraction, even for the total automated fingerprint identification system (AFIS). A fingerprint enhancement algorithm based on Gabor function and its application is developed in this paper. A method for ridge orientation acquirement is improved and a new method for ridge frequency acquirement is brought out. The formula that Gabor function is used in fingerprint enhancement is presented, and the fingerprint enhancement is implemented using ridge orientation and ridge frequency as parameters. The performance of this method is evaluated with some typical low quality images of Nanjing University fingerprint database. Experimental results indicate that the method has dramatic effect to low quality fingerprint images and false reject rate (FRR) of fingerprint matching can be effectively decreased after enhancement. Speed of the method can fill the demand of on-line AFIS.