Through the study on the environmental background features of the upper reaches of the Yanzse River, this paper approaches the importance of the construction of a shelter forest system and researches the disposition of a shelter forest system. On this basics,setting up a monitoring system for the ecological benefits of a watershed is designed. The results of the investigation show that after the disposition of a shelter forest system, the run-off on slops decreased 62%, the silt content dwindles 69%, the soil fertility and the microbe activity of the forest land are 4─5 times higher than those of the waste land, the ground and air temperatures in the forest land are 2─3℃ lower than those in the agricultural field, and the relative humidity is 30%─40% higher. The annual surface runoff and silt production will decrease 4.1mm and 5%─7% respectively if the forest coverage adds 1%. Moreover,biological methods can decrease 25% of the silt amount and engineering methods can lower 29% of the silt amount. In addition, the economic benefits also are very conspicuous after the construction of a shelter forest system. The net increase is 921.5─992.4 yuan/hm₂.a in the middle and low mountainous areas and it is 850.3─1438.6 yuan /hm₂.a in the Sichuan basin.