Abstract: In order to evaluate the purification capacities of DIN and DIP in different types of wetlands in two typical semi-closed bays (Jiaozhou bay and Daya bay) in China, a quantitative method of seawater-groundwater exchange was used to calculate the purification capacities. Results showed that: there are four wetland types in Jiaozhou bay, including sandy beaches, mud flats, estuarine intertidal zones and tidal marshes, and their purification capacities on DIN sort as follows: mud flats>sandy beaches>estuarine intertidal zones> tidal marshes and DIP sort as follows: sandy beaches>mud flats>estuarine intertidal zones> tidal marshes. The purification rate ranged from 2.11×10⁵ mol/d to 4.23×10⁵ mol/d for DIN and from 4.29×10² mol/d to 8.22×10² mol/d for DIP, respectively. The estimated nitrogen removal rate due to human activities such as land reclamation decreased by 3.1～5.4 t/d. In contrast, there are three wetland types such as mangrove swamps, sandy beaches and silt-sandy beaches in Daya bay. The DIN purification capacities in different types of wetlands in Daya bay sort as follows: mangrove swamps>sandy beaches>silt-sandy beaches, with an average of 4.22×10⁷ mol/d. Due to the area decrease of mangrove swamps and sandy wetlands in Daya bay, the decreased nitrogen removal rate was estimated to be 1.33×10² t/d and 0.81 t/d, respectively.