Abstract: In this paper,the effects of forest on protecting water sources are analyzed with“large basis comparision method.”The results of analysis are as follows:1.Because of the hydrologic effects of the forests,the run-off during the dry season increased by 80%,and the flow of the highest flood peat in a year decreased by 80%.Then the uniformity of the run-off during the period of a year improved by 30—40%.2.The forest soil has a better capacity of preserving rain water.There is a 32.5% increase of preserving rain water,48% increase of permeability and one-fold increase of dynamic capacity of preserving water in 1 meter of depth of the forest Soil.

Key words: total carbon, total nitrogen, total non-structural carbohydrates, soluble nitrogen, Phellodendron amurense, fine root