Perceptual learning is a phenomenon in which intensive training for a perceptual task may lead to significant improvement in the task performance. So far, the characteristics of the perceptual learning of facial expressions have not been investigated. In the current study, we trained subjects to distinguish facial expressions. With eight days of training, the subjects' discrimination performance improved significantly, and this improvement was generalized to faces with the same expression but different gender as the trained face. In the second experiment, we further examined the transfer of the learning effect between faces with different expression intensities. We found that the learning effect of happiness can be transferred from the high-intensity face to the low-intensity face, but the reverse was not true. Importantly, in all experiments, we measured the performance immediately after training and one month after training. The results showed that all learning effects and transfers were able to persist for at least one month, which implied that these findings revealed the long-term mechanisms of training. These results revealed the characteristics of facial expression learning and shed light on the mechanisms of perceptual learning for high-level vision.