Abstract: In order to reveal the action law of runoff and tide dynamics in the Lingdingyang Estuary, the main tide flux algorithm and the binary linear regression method are used to distinguish quantitatively the contributions of main dynamic factors to tidal flow velocities based on the fixed-point observation data over the years. The results show that the average flow velocity of the tidal cycle in the estuary has good correlation with tidal range, runoff and other dynamic factors and is always positively correlated with the tidal dynamics, but the contribution of the tidal dynamics has been weakened significantly in recent years. The runoff moved dominantly with the tidal current in the past, thus resulting in the decrease of tidal flow velocity. In recent years, however, the contribution of the runoff to the average tidal velocity becomes negative in the flood period and positive in the ebb period. Other dynamic factors mainly include vertical salt baroclinic gradient force and southwest monsoon. The contributions of these factors to the average tidal flow velocity in the main channel area are positive in the flood period and negative in the ebb period and have no significant changes. In the west beach waters, however, the contributions of these factors are opposite, showing negative in the flood period and positive in the ebb period. This is mainly related to the ‘tidal water capture’ and the energy storage mechanism present inherently in the beach waters. Thus, the Lingdingyang Estuary has more river-channel-type water flow dynamic characteristics than before. This is mainly related to the development of the estuarine toward a narrow and deep form caused by reclaiming and water deepening in the estuary in recent years.