本文基于2018年7月、10月和2019年2月在北部湾108°E以东、18°N以北区域的大面观测数据，分析了北部湾东北部的水团和流场特征。结果显示，研究区域水体特征存在明显季节变化：夏季水温北高南低，近岸低盐水占据30 m等深线以浅区域，海南岛西侧存在闭合冷水团；冬季水温北低南高，近岸低盐水退至湾顶10 m等深线以浅，湾内主要为混合水，海南岛西侧上层出现暖舌。海区流场基本为逆时针环流结构，流速大小存在季节变化，受风场影响明显；研究区与外海水交换不活跃，湾内水体不稳定性较强，冬季尤为明显，可能存在强垂向混合。

 Hydrological observations were carried out in the northeastern of Beibu Gulf in July and October 2018, February 2019 to reveal its seasonal variations. Sectional measurements of temperature, salinity and current velocity were deployed to the north of 18°N and east of 108°E. The results show that there is obvious seasonal disparities on the character of water masses in this region: the sea water temperature in summer decreases from northern shallow water to southern deep region and the onshore brackish water dominates the area shallower than 30 m, and a occlusive cold water mass appears in deep layer to the west of Hainan Island; while in winter the water temperature increases from north to south, the brackish water shrinks to the northern coast shallower than 10 m, the area is occupied mainly by the mixed water, and a warm tongue appears in upper layer on the west of Hainan Island. The circulation in the research region is mainly counterclockwise in all three seasons, though the strength of current varies in different seasons, and is significantly influenced by wind. The water exchange between the northeastern gulf and outer ocean is not active, since the observed salinity is entirely less than 34. The water mass is generally shear instable, and static instability appears in winter. This suggests that the diapycnal mixing in this region might be strong.