On the basis of survey of the movement law of watersediment and erosion and sedimentation environment at Qiqu Archipelago area where the deepwater harbor of Shanghai International Navigation Center lies, such problems as the lose of tidal discharge at bifurcations, the formation of sedimentation on sea bed at harbors and the change of erosion and sedimentation environment at Yangshan area, which were caused by the construction of dams at three bifurcations along Qiqu Archipelago, are studied in this paper. It is concluded in the paper that new situation has come into being after the construction of dams at bifurcations. As a result, the movement of water current, suspended sediments, and the erosion and sedimentation environment have been adjusted, previous balance between erosion and sedimentation will be resumed, the depth of the harbor will be kept well and the deepwater harbor will be constructed successfully.