Abstract: To evaluate trophic state and biotic community as well as the relationship between phytoplankton community composition and environmental factors in surface water of Ankang Reservoir, the water and phytoplankton were sampled monthly from January to December in 2012. The phytoplankton distribution and the physical and chemical indicators were analyzed. The characteristics of phytoplankton community were studied via Shannon diversity index (H) and Pielou evenness index (J). The trophic level was assessed via physical and chemical indicators, and trophic state index (TSI). One hundred and ten genera belonging to seven phyla were identified. The abundance of phytoplankton ranged from 0.11×10⁴ to 2.08×10⁴ cells·L^-1. The composition of phytoplankton and distribution of pollution indicator species, biodiversity and TSI indicated that surface water of Ankang Reservoir belonged to the ecological middling pollution type and was at a mesotrophic level. Highdensity feeding aquaculture and direct discharge of domestic wastewater had adverse effects on water quality. The water quality of Lanhe River, a tributary of Hanjiang River, was poor. Canonical correspondence analysis (CCA) showed that the impacts of the eight tested environmental factors on phytoplankton community composition and distribution varied in different seasons. Moreover, nitrogen was the main nutrient factor affecting the community composition of the phytoplankton. The physical and chemical indicators showed that the water quality of surface water of Ankang Reservoir was generally good and satisfied the standard of class Ⅱ water. However, the quality of total nitrogen poorer than the standard of class Ⅱ water in several sampling sites suggested that the water quality of Ankang Reservoir had the trend to be deteriorated.