Based on relevant literature and data, this paper analyzes the influence of forests on the annual flow in rivers. Conclusions derived thereupon can be summarized as follows.In most cases, the forest increases the average annual flow in rivers; only in a few cases does the forest decrease the annual flow. The increase of flow generally occurs in the dry or ordinary season, while the decrease of flow takes the form of decrease in the surface runoff, especially in the flood surface runoff in the flood season, resulting in mitigating the damage of floods. Therefore, whether the annual flow is increased or decreased by the influence of forests, its hydrological effects are favourable and are beneficial to agricultural production and people’s livelihood. The increase of flow resulting from the destruction of forests is, for the most part, the in crease of flood surface runoff, which will only bring about soil erosion and floods, causing harm to production and suffering to the people. From a longterm point of view, destroying forest vegetation can lead to the drying up of headwaters.