The physical factors such as topography，climate，soil，vegetation were described in this paper. By analysing the present situation and formative reasons of soil and water loss,, the authors 'advanced the principles，basis and system of division of forest for soil and water conservation and forest for water storage according to ecological benefit. Meanwhile，Wujiang watershed‘ (part in Sichuan province) was divided into, four different stereoscopic regions according to degree of soil and water loss a叫landforms in a. large range.