Abstract: In Rongcheng Swan lake, the sediments and Chaetomorpha were collected to study the changes of nitrogen and phosphorus contents in water under different microbial activities and algae conditions in the laboratory, and the influence of algal decomposition and microbial activity on the release of nutrients from the sediments was discussed.Under the condition without algae, the contents of total nitrogen and total phosphorus in water at different treatments changed at the range of 0.42~11.71 mg/L and 0.02~0.32 mg/L, which fluctuated over time during the experiment.In the middle and late stages, the order of nitrogen and phosphorus contents at different microbial treatments was mercuric chloride > glucose, control > formaldehyde.Under the condition with algal decomposition, the contents of total nitrogen and total phosphorus in water were much higher than those without algae, which ranged at 5.43~34.76 mg/L and 0.28~1.80 mg/L, respectively.The contents of nitrogen and phosphorus in water were high in the early stage, which decreased with time after that.In the early stage, total nitrogen and total phosphorus contents at different treatments followed the orders of mercuric chloride > glucose > control > formaldehyde and mercuric chloride > glucose, formaldehyde > control, respectively, while the difference among treatments decreased at the late period.Under the same microbial activity, the contents of nitrogen and phosphorus with algae were significantly higher than those without algae.At the end of experiment, microbial activities in sediments were relatively high under the condition with algae, which followed the order of control > glucose, mercuric chloride >> formaldehyde.Under the condition with algal decomposition, microbial activity had a significant effect on nitrogen and phosphorus releases from the sediments in Swan lake.The release amount of nitrogen and phosphorus from the sediments was high when microbial activity was stronger.