Abstract: The thermal structures of the Bohai Sea and the Huanghai Sea are analyzed by observations and simulated by POM model with monthly mean wind stress and weekly surface water temperature as exter nal forcing respectively.The thermal structure is characteristic homogeneous winter style from October to March of the next year,but is stratified structure(consists of mixed layer,thermocline and tidal mixed layer) summer style from May to August,April and November are transition periods of both styles.The lowest water temperature occurs in February for the whole water column,the highest occurs in August for the surface layer and in November to October for bottom layer.Except for some similar thermal structure between the Bohai Sea and coastal shallow water zone of the Huanghai Sea,for the thermal structure of deep water area in central trough,the Huanghai Sea Cold Water Mass and the Huanghai Sea Warm Current are two special factors.As for effect on the deep water,the former is significant in summer,the later is significant in winter,so that the low layer water appears to be cold in summer,while warm in winter compared with the environment,basically is converse to annual variation of SST.As for the three-dimensional structure of above area,compared with the Bohai Sea,the period of homogeneous structure(from January to March) is shorter and the period of stratified structure(from May to October) is longer,the amplitude of annual variation of low water temperature is smaller(no more than 5) and the intensity of the thermocline layer is stronger.The simulated result shows that the driving power of the Huanghai Sea Warm Current is monsoon circulation,and therefore the question whether there is some dynamic effect on the for mulation and development of the Huanghai Sea Cold Water Mass is deduced.