Abstract: The Southern Tianjin Plain, located in the western coast of Bohai Bay, is an ideal natural place to study the transgression and sea level change. Based on the comprehensive research of sedimentary characteristics, dating (AMS ¹⁴C) and micro paleontology of two boreholes (ZKQ1 and ZK1), the authors inferred that transgression maximum influence boundary in the MIS 3 stage was between two boreholes (ZK1 and ZKQ1). The western side of the boundary is continental sedimentary, and the eastern side of the boundary is transitional sedimentary. boundry location was in the area of the present Heilonggang River and was once an ancient river channel, so it is speculated that the area affected by the transgression in this period was restricted by the ancient river channel. Combined with the previous three boreholes (ZKQ4, CGZ5 and CGZ7) data, the author has established the profile of the E→W direction (sea → land) and further confirmed that E→W in this area was transformed from Marine facies (CGZ7 and CGZ5) to transitional sedimentary (ZKQ4 and ZKQ1) to continental facies (ZK1). It is speculated that the transgression boundary of MIS3 is in the area of Dongshangmatou (CGZ5) and Gaojiazhuang (ZKQ4) in Jinghai district. This achievement is of great significance to the restoration of paleogeographic evolution, the sea-level change research and the geological exploration of hydraulic environment in this region.