Denitrification in anaerobic lake bottom sediments and leachate providing carbon source via flocculated algae were simulated in the laboratory.TN,ammonium,nitrite,nitrate,volatile fatty acids (VFAs),COD,electric potential and pH were analyzed to confirm that the denitrification in sediments was truly promoted by small molecular compounds such as VFAs which were reduced from the plentiful biodegradable carbon in algae.The maximum VFAs content in 2×algae system and 1×algae system were 2232.96 and 1263.36 μl/L,respectively.The maximum TN removal ratio was about 42.1%,nearly 2.43 times of the control.The carbon of flocculated algae is available for heterotrophic microbes but needs some time to be transformed.A sustaining COD reduction rate showed in all the added algae systems after low COD reduction rate,positive electric potential and increasing nitrate had last in them for about 4 days.The maximum COD reduction rate of 2×algae system,1×algae system and the control was 42.08%,32.93% and 14.46%,respectively.The degradation of algae generated VFAs can be directly used by denitrifying bacteria to facilitate denitrification process.The effect that flocculated algae cell as carbon source can promote sediment denitrifying process was verified,and the influence of flocculated algae on C and N of sediments was analyzed.The study could provide technical basis for reducing the internal nitrogen in sediments of eutrophic lakes.