Normal>Dawuzhuang oyster reef is the deeply studied one in the recent years while Konggang oyster reef is a new one on the northwest coast of Bohai Bay. The Dawuzhuang oyster reef grew up to the middle to upper parts of intertidal zone in the year 5 520 cal BP, and development stopped with the gradual disappearance of the marine influence. The author speculated that the seawater completely withdraw from the two reefs were later than 4 700 and 1 100 years ago. It was speculated that the relative sea level were 2.95 m under the modem sea level in 4 700 a ago and 1.5 m under the modem sea level in 1 100 a ago. This is due to the crest decline and compaction which indicated that the earlier of the regression, the lower position of the upper limit of the marine layer in the west Bohai Bay. The ancient Yellow River diverged and into the sea from Tianjin in 4 000 years ago. At the same time, the large number of the sediments into the sea and made the coastline constantly advanced seaward which lead to the subsequent oyster reefs developed seaward.