Abstract: This study analyzes the past 55 years (1960-2014) decadal tidal characteristics of the four tidal stations of the Ou-jiang estuary, and explores the affecting factors and the possible reasons that caused those variations. The results show the tidal characteristics of Longwan tidal station had no obvious changes in the period. Wenzhou, Meiao and Huayantou station were presented similar tidal characteristics, which includes the rising high tide levels, declining low tide levels, increasing tidal ranges, extending flood time and shorting ebb time. It seems the basin runoff changes didn’t effect on those estuarine tidal characteristics. The main reasons that caused regional tide variations were human activities such as embankment constructing and cultivation in former water areas. The tidal changes at Wenzhou, Meiao and Huayantou station were most due to the intensive river sand exploitations. So the Ou-jiang estuary project design and water managements should be considered sections separately.