Abstract: Mangroves have many functions, such as promoting siltation and protecting beaches, consolidating embankments, resisting ecological risks and maintaining ecological balance. They have obvious advantages and special contributions in purifying water and improving environmental quality. In order to explore the mitigation ability of mangroves on water eutrophication, this study took artificial Kandelia obovata forests with different stand ages at Yundang Lake as the object, and determined the contents of nitrogen (N) and phosphorus (P) in their organs and litter, estimated the total amount of N and P absorbed by mangroves. Results showed that with the increase of stand age, the average N and P contents in plant organs and litter increased significantly, especially in plant leaves and litter leaves. From the mangrove planting in 1999 to 2013, the total amount of N and P absorbed by mangroves at Yundang Lake in form of existing biomass was 1 948.83 and 178.61 kg, respectively. The total amount of N and P returned was 7.47 and 0.58 kg and the total absorption of N and P was 201.68 and 19.57 kg, respectively, in 2013. Mangroves can absorb N and P, which can alleviate the eutrophication of Yundang Lake.