Based on field data in half a month during flood and dry seasons by four observation stations deployed in the inner Lingdingyang bay，the temporal and spatial variation characteristics of residual currents and net flux are analyzed，and the action laws of the main dynamic factors are discussed.The study shows that depth-averaged residual velocities in half a month are less than 10 cm/s during flood season and 5 cm/s during dry season with directions generally pointed the offshore.Net flux in the bay head waters is transported from west to east in both flood and dry season，and is strongly positively correlated with runoff dynamics.After receiving the water and sand from the shoals on the east and west sides of the main trough，the water and sand are always transported to the southwest sea.However，the directions of net flux transportation would change from pointing offshore during flood season to upstream during dry season，and both are positively correlated with the runoff dynamics.The north waters of Qi′ao island in the west beach would be in a siltation state all along for continuous input of net flux in both flood and dry season.The multiple linear regression method is used to fit water surface residual currents and main dynamic factors in the main channel waters.The results show that water and sediment in surface layers would be drove to move upstream by tidal power，and downstream during flood season and upstream during dry season by runoff power，while wind power drive surface water and sand to keep consistent with its own direction.The constants in the fitting formula reflect the southwestward transportation law of surface water and sediment in the inner Lingdingyang bay under the comprehensive action of geostrophic Coriolis force and so on with more obvious in dry season.