Abstract: In order to find out the water quality changes during algae bloom and non-algae bloom in the upstream of Xinglinwan Reservoir in Xiamen,17 factors(temperature, pH, Redox potential, dissolved oxygen and salinity, conductivity, turbidity and transparency,the concentration of chlorophyll a and total carbon, total organic carbon, total nitrogen, ammonium nitrogen, nitrate nitrogen, nitrite nitrogen, total phosphorus and Orthophosphate)were determined. The results showed that the chlorophyll a concentration in the bloom period and non-bloom period were 121.31 ± 18.89(μg/L) and 28.53 ± 2.82(μg/L) respectively, and the difference between the two was very significant (P<0.01), and there was no significant correlation between the physiochemical factors and chlorophyll a of the two periods (P>0.05). Except for the water temperature, Redox potential, ammonium nitrogen, total phosphorus and Orthophosphate, the differences of the physiochemical factors in the two periods were significant (P<0.05) or very significant difference (P<0.01). In addition, the comprehensive nutrition index of the bloom period and the non-bloom period were 78.32 ± 2.63 and 72.24 ± 2.57, respectively. It can be concluded that the water was in severe eutrophication during these two periods.