Abstract: Based on the data collected at 312 stations in the northern Bohai Bay during summer, horizontal and vertical distribution of SPM concentrations were described in this paper. The mass concentrations of SPM exhibits a horizontal distribution with high values inshore and at bottom and low values offshore and on the surface, In the vertical direction, the volume concentration of SPM can be divided into two types:one with a sharp peak at depth of 10 to 15 m and the other without the peak. The peak at the thermocline depth was supposed to be caused by accumulation of biological matters as a result of rich nutrients trapped by water of low diffusion.