Abstract: The signiflcant test for the physicochemical characters at different summer water levels in Heilongtan Reservoir was canied out and the input and variation of physicochemical characters analysed comparatively.It showed in input higher contents of conductivity, hardness, NO3-, TN and Mg2+, SO, Ca, lower contents of CODCr,and NH4+ were observed at high summer water level.The gradient of physicochemical characters was greater at high summer water level than that at low summer water level.