Abstract: Together with previous data of surface diatoms from 15 stations,the authors analyzed surface diatoms from 14 stations along four 2~3 km long sampling lines in the intertidal zone of the Bohai Bay, and found 46 species which belong to 21 genera. The surface diatoms in the intertidal zone and shallow sea of the Bohai Bay can be divided into three assemblages with the Correspondence Analytical Method. Assemblage Ⅰ, Cyclotella striata/stylorum-Coscinodiscus spp., is distributed in the mud-dominated intertidal zone; Assemblage Ⅱ, Amphora spp.-Achnanthes spp., spreads in the sand-dominated intertidal zone; and Assemblage Ⅲ, Cyclotella striata/stylorum-Nitzschia spp.-Coscinodiscus spp.-Palaria sulcata, exists in the shallow sea. From the intertidal zone to the shallow sea, the percentage of Cyclotella striata/stylorum reduces and the percentage of Palaria sulcata increased with the water depth.