Abstract: In biogeochemical circulation in coastal wetlands of southern Laizhou Bay, the main sources of N and P are industrial and municipal domestic wastewater, surface runoff and superfluous irrigation water from farmlands as well as fishery wastewater. N and P are transported into subtidal wetlands through intertidal and supratidal wetlands, which lead to concentrations of inorganic N and P of seawater rise in subtidal wetlands. This study shows that N and P load in coastal wetlands of southern Laizhou Bay are 46 271.1 tons and 2 092.1 tons in of 2000. Through analysis of the processes of biogeochemical circulation in the coastal wetlands of southern Laizhou Bay, it is discovered that natural coastal wetlands absorb and decompose N and P. Observed concentrations of inorganic N and P in seawater of subtidal wetlands for the year of 2000 are respectively 0.086 mg·L^-1and 0.029 mg·L^-1, while theoretical concentrations are 6.74 mg·L^-1and 0.299 mg·L^-1without regard to N and P absorption by intertidal and supratidal wetlands respectively, 78.4 and 10.3 times of observed concentrations,indicating obvious absorbing and purifying effect of natural wetland on input N and P. To decrease the concentration of N and P in the seawaters of southern Laizhou Bay, we need to develope circular economy, decrease the amount of N and P load in coastal wetlands, protect and restore natural wetlands, construct artificial wetlands and enhance purifye functions.