This paper focuses on two key problems in automated fingerprint identification system (AFIS): fingerprint image enhancement and minutia matching. A fingerprint image enhancement algorithm is proposed based on orientation field. In addition, a minutia matching algorithm is proposed which modified the algorithm presented by Jain et al. About this algorithm, a simpler alignment method is used. Ridge information is introduced into the minutia matching process in a simple but effective way. One of the advantages of doing so is to solve the problem of refence point pair selection with low computationl cost.Iakkition,the changeable sized boundary box is used to make this algorithm mote robust ti nonlinear deformation between fingerprint images.Experiments are done on the FVC2000 databases with the FVC2000 performance evaluation method and the results show that this improved algorithm is better than the originalone.