The ecosystem change of external forcing, course system, system output of ecosystem in the frame of conception model of the migrants resettled area in Three Gorg es reservoir area is analyzed. In typical watershed, Quxi watershed, the result of external forcing, submerge and migrant, is the resource change of slope cultiva ted lands, economical fo rest, vegetation, water, habitant etc. of the eco system, and the changes of demand for food supplies, energy resource and education. By the action of feedback mechanism, the system outputs are soil and water loss pricking up, biological diversity being destroyed, heavily soil degrading etc. . And then brings forward some countermeasures such as developing watershed management,resuming and rebuilding mountainous region ecosystem, streng thening research on reforestation countermeasure, to easeup the conflict between human and land and achieve the sustainable development.