The quantities of bacterioplankton and Chl-a were invested in Bohai Bay from May 2005 to October 2005.The results showed that the correlativity between bacterial abundance and Chl-a's concentration was high in October(r=0.845,p0.01) in surface layer water of Bohai Bay.The percentage of marine bacterial biomass was 0.355%～56.25% during the primary productivity of phytoplankton;The spatial change of BB/PB was higher in offshore than inshore.Exogenous organic matter was an important factor in controlling the distribution of bacterioplankton in August,but it was primary production in October.