Under the background of the climate warming and sea-level rising, the bay transgression in the Holocene is dominated by marine dynamic,and the information which recorded the sea-level changes may be more abundant. Studying the type and extent of transgressions in the Holocene can provide the basis for predicting the transgression of the gulf. The HG01 borehole is located in the northwest coast of Bohai Bay (39°28'21.16"N, 118°01'16.50"E), about 28km from the modern coastline. 85 samples were collected from the depth of about 20 ~ 0m at 20 ~ 40cm intervals. The results of AMS ~(14)C dating show that the formation we study covers the time period since the Late Pleistocene. All samples were analyzed and identified for quantitative statistic of foraminifera and ostracod microfossils. The abundance and diversity of microfossils were calculated later and 65 species of 24 genera of foraminifera and 39 species of 27 genera of ostracodes were found. According to the vertical distribution characteristics of micropaleontology and their indicators of the sedimentary environments of the northwest coast of Bohai Bay, combined with sedimentary characteristics, HG01 borehole (20m to shallow) is divided into 6 microfossil assemblages and a fossil spacer, indicating the different sedimentary environments, from the bottom to top as follows: The depth of 19.4~17.0m (MIS 3) is the river mouth identified by the lower abundance and diversity of foraminifer fossils and the olive yellow fine sand including the fragments of oyster. The depth of 17.0~10.0m,aged the early period of the Last Deglaciation (18.0~11.4cal.ka B.P.). The lower part (17.0 ~12.9m) is the floodplain identified by the lack of microfossil and sedimentary characteristics. The upper part (12.9 ~ 10.0m) is the freshwater swamp identified by freshwater ostracodes. The depth of 10.0~8.2m dated the Early Holocene(11.4-8. Ocal.ka B.P.). In this period, foraminifera and terrestrial ostracoda are coexisting, but the number of microfossils is few. This period is the coastal lacustrine. The depth of 8.2 ~1.3m dated the Middle Holocene(8.0~6. Ocal.ka B.P.). In the lower part (8.2~3.5m),abundance and diversity of microfossils are relatively large, and the overall upward trend is from bottom to top. This period is the lagoon. In the upper part (3.5 ~1.3m),the abundance and diversity of microfossils reached the maximum and this period is the coastal sand bar. The depth of 1.3~0.5m aged the Middle-Late Holocene (6. Ocal.ka B.P. to present). In this period, the abundance and divergence of the microfossils showed a decreasing tendency from bottom to the top,and there werea few terrestrial ostracodes in the upper part. This period is the supralittoral zone.