Fingerprint image preprocessing is the basis for fingerprint identification which has a direct impact on the success of fingerprint identification. The existence of sudoriferous pores effects the step of binarization and thinning which makes the ridge line into two parts, leading to negative impact on the extraction of true minutia by making lots of false minutia points in the next steps, so the step of repairing the sudoriferous pores is very important. The gray mutation of the middle part of the ridge line which caused by sudoriferous pores can be repaired by sudoriferous pore restoration, thus avoiding the split up of fingerprint line after thinning. Therefore, this step reduces the number of false minutia points.