With the rapid development of social economy, the agricultural non-point source pollution has become one of the main contributors to the deterioration of water quality and eutrophication of water bodies. The riparian buffers play an important role in purifying water quality, which are considered as one of best management practices (BMPs). The main results of research on the purification mechanism of the riparian buffers, as well as on the influencing factors for the effectiveness of purification, are systematically summarized in this paper. Based on the defects of previous studies, some suggestions are proposed, including broadening the range of research on purification mechanism of the riparian buffers, not limited to the nutrients and surface runoff. Besides, not merely natural factors, but also human factors should be taken into account when it turns to the influencing factors for the effectiveness of purification.