A nine-day observation on the process of vertical stratification of physicochemical variables was taken from 24th July to 1st August, 2010 in Lake Taihu,a large shallow lake of China.Frequent stratification processes occurred during the 9 days.But the stratifying state was unstable,and normally last less than 1 day.The main factors causing stratification were water temperature and its diel variation, cyanobacterial bloom scum and wind-induced wave disturbance.The vertical difference of water temperature-may reached 3.94℃,which was mainly influenced by diel variation of air temperature and solar radiation.And the stratification of water temperature was the basic factor causing the stratification of dissolved oxygen,electric conductivity,and pH.Cyanobacterial bloom scum could cause the strongest stratification, which could cause vertical difference of 8.67mg/L of dissolved oxygen, 48μC/cm of electric conductivity, 1.49 of pH, 9.1μg/L of chlorophyll-a and 26.5NTU of turbidity.Besides turbidity,stratification of physicochemical variables became weaker with the increase of wind speed.No stratification happened during strong wind period in which of wind speed over 6m/s,while it often happened during weak condition in which of wind speed less than 2m/s.The study indicated that,stratification processes could frequently short-term occurred in large shallow lakes,and might have potential influences on the processes of biological activities and exchange on air-water interface and water-sediment interface.