Abstract: Effects of forest filter means that forests can eliminate and/or buffer contamination. This is one of the important service functions of forest ecosystems. With the increase of pollution to water body and the air, more and more expectations have been paid to the self-cleaning function of forest ecosystem.Therefore, it is very necessary to study the process and mechanism of forest ecosystems to hold, absorb, and purify pollutants with their canopy, tree trunks, shrubs, herbs, litter and soil（microbe）. It is also an important step for assessing the hydrological service functions of forests. In this paper, effects of forest ecosystems to purify pollutants, specially acid deposition by tree layer, undergrowth, the litter and the soil were reviewed in order to find out the existing problems of current research and look for the possible approaches for further research. It was found that most research focused on the experimental observations and the phenomenon explanation and there was a lack of research on the allocation process and reasonable simulation models.In this paper, the authors took the whole forest as a filter system, and described the research progress in different subsystems, including plants, litter, soil and microorganism.

Key words: forest ecosystem, forest, filter, elimination and buffering function