[Objective] The influencing factors of water environment change and its improvement countermeasures in Danjiangkou reservoir area after the operation of the middle route of south-to-north water diversion project were studied in order to provide reference for reducing pollution load and ensuring water quality safety in the reservoir area.[Methods] Taking Danjiangkou reservoir and the upper reaches of the river basin as the study area, the characteristics of water environment change and its main influencing factors were analyzed by using the before and after comparison methods, and the countermeasures to protect and improve water environment were proposed.[Results] After impoundment of the dam, the water quality of Danjiang Reservoir area was generally good, but the spatial difference was significant. Some tributaries and bays were polluted seriously, and the contents of nitrogen, phosphorus and some heavy metals were high.[Conclusion] Soil and water loss, point source pollution in rural areas, non-point source pollution in agriculture and human activities are the main factors affecting water quality in Danjiangkou reservoir area. In view of the ecological environment problems existing in the reservoir area, the protection countermeasures and suggestions are proposed, such as continuous and stable implementation of the policy of returning farmland to forest or grassland, the optimization of the rural industrial structure, the strengthening of the supervision of industrial and mining enterprises' pollution discharge, the optimization of monitoring stations and the strengthenomg the residents' environmental protection awareness.