There are three basical vertical distribution patterns of suspended matter in seawater in the South Yellow Sea: even distribution with high concentration, positive gradient distribution and double gradient distribution. An important phenomenon in the seawater is the spring layer of suspended matter below the density layer where the concentration of suspended matter rapidly increases and forms the turbid water layer affecting greatly seawater physical parameters especially density. The density of seawater with suspended matter, called unit weight in situ of seawater, is a function of temerature, salinity, water depth and concentration of suspended matter, and can be calculated as density of seawater plus unit weight of noncombustibles in suspended matter.