Water circulation and sediment transport in the Beibu Gulf are important for its environmental protection and resource exploitation.By employing the Regional Ocean Modeling System(ROMS),we studied the seasonal variation of circulation,sediment transport and long-term morphological evolution in the Beibu Gulf.The simulation results show that the circulation induced by tide and wind is cyclonic both in winter and summer in the gulf and that the wind-driven circulation is stronger in winter than that in summer.The sediment concentration is higher in the Qiongzhou Strait,west of the Hainan Island and the coast of Vietnam and the Leizhou Peninsula.The sediment is transported westwards in winter and eastwards in summer in the Qiongzhou Strait.The west entrance of the Qiongzhou Strait is dominated by westward transport all the year round.The sediment discharged by rivers is deposited near the river mouths.The simulated result demonstrates that the sediment transport is mainly controlled by tidal induced bottom resuspension in the Beibu Gulf.Four characteristics are summarized for the distribution patterns of erosion and deposition.(1) The erosion and deposition are insignificant in most area of the gulf.(2) Sediment deposition is more significant in the mouths of Qiongzhou Strait.(3) The erosion is observed in the seabed of Qiongzhou Strait.(4) Erosion and deposition occur alternatively in the west of Hainan Island. Water circulation and sediment transport in the Beibu Gulf are important for its environmental protection and resource exploitation. By employing the Regional Ocean Modeling System (ROMS), we studied the seasonal variation of circulation, sediment transport and long-term morphological evolution in the Beibu Gulf The simulation results show that the circulation by by and wind is cyclonic both in winter and summer in the gulf and that the wind-driven circulation is is in winter than that in summer. The sediment concentration is higher in the Qiongzhou Strait, west of the Hainan Island and the coast of Vietnam and the Leizhou Peninsula. sediment is carried westwards in winter and eastwards in summer in the Qiongzhou Strait. west entrance of the Qiongzhou Strait is dominated by westward transport all the year round. The sediment by rivers is deposited near the river mouths.The simulated result demonstrates that the sediment transport is mainly controlled by ti (2) Sediment deposition is more significant in the mouths of (3) The erosion is observed in the seabed of Qiongzhou Strait. (4) Erosion and deposition occur alternatively in the west of Hainan Island. Qiongzhou Strait.