Abstract: A sea breeze event occurs on 21 August 2006 when a cold front passes Shandong Province and the synoptic scale wind is northerly. In order to analyze the development of the sea breeze, the feature of the sea breeze is analyzed with 123 AWS data in Shandong Province, over 30 AWS station data in Qingdao area, in the island and three buoys in the sailing spots. As a result, the detailed AWS station data in the coastal area and buoys can give more detailed and new feature of the sea breeze. Further more, these data are assimilated into the ARPS (the Advanced Regional Prediction System) model. The controlled experiment uses 2 level 1 way nested grids, with the horizontal resolutions of 30 km and 6 km respectively. In vertical, a scheme consisting of 53 sigma z levels with a minimum thickness layer of about 20 m near the surface and vertically stretched grids extending to model tops at about 20 km height is used. Compared with the observation, the model can simulate development of the sea breeze reasonably. With the observation and the simulation, the detailed feature of the boundary wind and 3 dimension structure of the sea breeze are analyzed, indicating that the sea land temperature difference of around 2 ℃ causes the sea breeze in this case. Under the northerly wind, the surface temperature to the south of Qingdao rises faster than that on the north land, thus the sea breeze mainly occurs in the southeast coastal region. The sea breeze begins offshore and then develops into the land and the far ocean widely. The vertical height of the sea breeze circulation is as shallow as below 500 m. Due to the stronger offshore synoptic scale wind the sea breeze can only spread to very limited area along the coastal line. The northerly synoptic wind passes over the Bohai Sea and causes cold surge to land in Shandong Province, which is adverse for the sea breeze maintaining, as a result, the sea breeze in the southeast coastal region of Shandong Province dies earlier at around 17:00. When the sea breeze begins the reverse circulation forms around 1500—2500 m height at the same time. But the vertical circulation doesn't develop clearly until the evening and the height of it is below 1000 m. The vertical circulation and the reverse circulation can last 3 hours after the sea breeze dies.