Abstract: This paper deals with the synchronous characteristics of cheniers existing on the Chenier Plain along the west coast of Bohai Bay and oyster reefs existing on the Oyster Reef Plain of northwest Bohai Bay and its adjacent shallow sea. Approximately, such synchronous processes can be separated into six periods, alternately intercalated with the Holocene cold events of 5, 4, 3, 2 and 1. The vertical range between front-foot and rear-base of the chenier-bottom corresponds to the vertical 3m contemporaneous high tidal range, and the reef top approximately reflects the MSL (mean sea level). Since 7ka cal BP, the relative sea level trend in the Chenier Plain has been quite similar to the present situation, with possible small fluctuations being less than ±1m. The Mid-Holocene high stand of the relative sea level was offset by sedimentary consolidation. However, under the joint influences of neotectonic subsidence and consolidation, the relative MSL was 2~3m below the present sea level on the Oyster Reef Plain.