In the context of climate change，extreme weather and water level events occur frequently.To study the long-term evolution characteristics of extreme tide levels in the Yangtze Estuary，this paper analyzes the tendency and the return period of the extreme tide level in the Yangtze Estuary based on the methods of the extreme value theory，using the observed data in the last 33 years.The results show that the annual extreme water level at Xuliujing station shows a slight downward trend，which is directly caused by the decrease of local mean sea level due to the reduced river discharge of Datong station.The storm tide level caused by Typhoon Winnie in the Yangtze Estuary is estimated to be a once-in-a-century event according to the Block Maximum model.However，it is projected to occur once in 60 years based on the results of the POT model，with the once-in-a-century return period tide level reaching 7.0 m.Calculation of the return period of tide level is essentially a process of replacing probability with frequency and extrapolating from sample to the whole，with a certain degree of uncertainty.Its significance lies in using obtainable data to calculate the risk rate of an event，providing a basis for engineering design or risk management.