Abstract: Since 2005, nearly 3000 hm² water area were reclaimed in Qinzhou bay, change of shoreline is very significant.By a 2D numerical simulation of tidal current in Qinzhou bay, influence of shoreline change on dynamics and water exchange in Maowei sea, upstream of Qinzhou bay were discussed form aspect of tide current characteristics, tidal flux and water change, etc.Among them, the exchange period of water is characterized by a half exchange time of total load, to avoid the deviation caused by position of sampling points in single point concentration half exchange time, and the deviation caused by water volume difference at different tide period in average concentration half exchange time.The results show that:by the change of shoreline, mouth of Qinzhou bay narrowed further and tidal volume of it decreased; to the Maowei sea, the tidal range and flow velocity decreased, the tidal flux diminished 1.30%~1.53%, and the half-exchange period increased 51 hours, the tide and water exchange capacity were weakened.