To explore the regular pattern of reservoir water quality variation and its influenced factors of Xin'anjiang Reservoir,we comprehensively analyzed the spatial-temporal variations of water quality in Xin'anjiang Reservoir(Lake Qiandao) using the water quality data monitored monthly during 2009-2010 and literature.The results showed that an obvious seasonal variation of transparency was caused by the interaction effects among hydrology,organism,and human production activities cause,total nitrogen,total phosphorus and chlorophyll.Especially in the upstream-Jiekou transect,its seasonal change of each indicator is significantly different.The water quality of the upstream was not same to the downstream water quality obviously with low transparency,high content of nitrogen,phosphorus and chlorophyll.This reflects that exogenous supply and human activities have a primary contribution to water pollution.Thus,the water quality could be improved by controlling the exogenous pollution.The main factor that influences transparency of sensory indicators is the algal biomass,while the factor which controls the algae biomass change is the content of nitrogen and phosphorus.Therefore,strictly controlling the quantity of phytoplankton cells is the key to solve water environmental problems of Xin'anjiang Reservoir.In addition,the economical fishing quantity and inventory of Xin'anjiang Reservoir has certain association with water quality and the inverse correlation was found between the annual fishing quantity and water transparency.Therefore,we should pay more attention to the fisheries management and make a scientific and reasonable fishery culture pattern to keep development of Xin'anjiang Reservoir resources sustainable.