Abstract: The eco-environment of Manwan reservoir is frail and apt to deterioration because of its abrupt slope,developed faults,topographic unconformity and concentrated rainfall.Based on site investigation and statistics analysis.It is elaborated on several aspects of the reservoir’s ecological degradation:① landscape change.Villages,cropland,terrestrial life formerly in the valley blow the elevation of 994m were inundated;while forest,grassland and grading slope from 1000m to 1800m were replaced by newly-reclaimed sloping fields and newly-established concentrated settlements.The eco-environment tends to be frailer,whereas the reservoir’s hydrothermal change after impounding provides better conditions for vegetation from 1000 to 1300m,hence contributes to its restoration;② After 1984,soil erosion in the slope land around the reservoir area have been more serious.The annual sediment concentration in the river flow was increased by 36.6%,and annual sediment flow increased by 37.3%;③ serious loss of the reservoir’s storage capacity.According to the survey in 1998,after 3 years’operating,the loss of the active storage reached at the level that expected after 15 years of operation;④ frequent occurrences of soil-and-water loss,landslide,mudflow,torrential flood as well as collapse. Based on further analysis on human factors leading to ecological deterioration,it could be found that:① slope reclamation brings about the loss of vegetation and the worsening of soil erosion;② filling and releasing of reservoir make the surrounding area less stable and be apt to collapse and landslide;③ infrastructure development of highway and irrigation projects results in landslide and mudflow;④ the reservoir’s sediment concentration and water pollution are closely related to upstream environmental depression.Finally,to reduce the ecological deterioration’s negative effect on local production,life as well as the reservoir’s economic life,and to maintain the ecosystem of the reservoir and improve the local farmers’life conditions,five countermeasures have been put forward:① resettle those who reside in the deteriorated area and those who suffer from landslide and mudflow in places beyond the reservoir area.Currently,the affected population is about 1000,with a resettlement cost of 30 million;② regarding small basin as ecological unit,combine reasonable land use,disaster control and community development together to carry out comprehensive regulation,with emphasis on Gonglang River in Nanjian and Heihe River in Fengqing county;③ strengthen the harnessing of resettlement areas and key disaster-hazard regions;④ increase maintenance cost for Manwan hydropower station,supporting afforestation engineering,rural resources exploitation and poverty alleviation programme in resettlement areas;⑤ harness water-contaminating enterprises in Dali city and Lanping county to improve the inflow quality;⑥ along with the construction of Xiaowan’s large-scale power station,speed up natural forest engineering and soil-and-water loss control along banks of upper-and mid-Lancang River.