Using the data specially observed on the Bohai Sea oil platform by the authors for studying thermocline for two weeks,the thermocline depth,the temperature and the salinity of the layers below and above the thermocline were numerically modelled.The model is based on the Stigebrandt model and some important supplements are made in this paper in accordance with the local condition of the sea.The modelling results fit well in the observations.It is proved that the entrainmem due to both the tide and the wind can give rise to rather intense mixing cross the thermocline.This process makes the temperature rising below the thermocline,and causes the nutrient increasing above it,which has important significance for the marine physical environment and the marine organism.