Abstract: Hydrological factors of formation of large flood in the lower tidal reach of the Yangtze River are analyzed,and change trend of large flood is revealed.Obtained conclusions are:(1) Formation of large flood in the river reach is very complex; (2) Occurrence frequency of large flood in the river reach has been increasing since 1900; (3) The mean value of the peak stage has been rising since 1975; and (4) Above the charct eristics of occurrence of large flood in the river reach are primarily affected by human activity and rise of sea level.