Abstract: Using fuzzy evaluation the annual variation of water quality in four monitoring areas of Yantan Reservoir was evalualed. The results showed that the annual variation of water quality in Yantan reservoir was at grade 芋, the main influence factor was total nitrogen(TN), the analysis of TN exceeded multiple (WTN) indicated that at the same grade (grade 芋), the water quality of Hada monitoring area was the best, WTN ranged from 0.096 to 0.883; the water quality of Jiangdong monitoring area was the worst, the WTN ranged from 0.557 to 1.358. The annual variation of water quality had a close relationship with the condition of large aquaculture area, we should protect the water environment, improve the level of large waters resources爷comprehensive and sustainable utilization when we developed the large aquaculture and promoted the income of immigrants in reservior area.