Using the theory of restoration ecology, and regarding the sustainable development of region as the main object, combineing with the present condition of withdrawing from farming to afforesting and grass planting in the middle and lower reaches of Tarim river, this put forward the evaluation index system and evaluation model of compositive ecological benefit of ecological project of withdrawing from farming to afforesting and grass planting in the middle and lower reaches of Tarim river. The evaluation index system includes 11 indices relating to biologi- cal benefit, soil benefit, small climate benefit and hydrological benefit. Applying analytic hierarchy process (AHP) evaluated ecological benefit of ecological forest, economic forest and herbage grassland and also compared with farmland ecosystem. The result indicated that compositive ecological benefit index of ecological forest 9 eco- nomic forest and herbage grassland ecosystem larger than farmland ecosystem and the order of ecological benefit is economic forest>ecological forest>herbage grassland>farmland ecosystem. Therefore the paper proposes some scientific suggestion of planning, overall arrangement, sort of tree and grass of ecological project withdrawing from farming to afforesting and grass planting in the middle and lower reaches of Tarim River.