The effect of thermal stratification and its relationship with water quality was researched by field observation in this study. Through the assessing of the degree of thermal stratification by calculating the dimensionless parameter of thermal resistance to mixing (RTRM) indices from 2008 to 2010, it indicated that the waterbody of Xiangxi River were stratified strongly in the summer months. The analysis of the degree of thermal stratification with both the meteorological and hydrodynamics factors showed thermal stratification intensity was more sensitivity with meteorological factors in Xiangxi River. Through the analysis of the relationship between thermal stratification and water quality, the results indicated that the concentration of Chlorophyll a was higher in the epilimnion affected by the thermal stratification, which could cause algae bloom. The results may further help to evaluate the thermal stratification role in eutrophication process and algal blooms formation in Xiangxi River.