The phycial and chemical characteristics of the surface sediment of Lake Xuanwu, Nanjing were investi-gated in April-September, 2004 and April-July, 2005. After simulating the phosphorus release in laboratory fromthe surface sediments samples under static conditions under 5, 10, 15,25,35℃, respectively, the release fluxes ofphosphorus across the water-sediment interface in different sub-lakes of Lake Xuanxu were calculated, i. e.0.815 t/a, 1.013 t/a and 0.266 t/a for northern, southeastern and southwestern sub-lakes, separately. The totalrelease flux for Lake Xuanwu could be 2. 094 t/a. Based on the Fick's Law, a pore water dispersion model wasbuild up, and the phosphorus release for the whole Lake Xuan could be calculated as 2. 014 t/a to the water, with0.799 t/a, 0. 983 t/a and 0. 232 t/a for northern, southeastern and southwestern sub-lakes. Such a net releasefrom lake sediment for phosphorus makes an appropriate 0, 101 m/L in lake water-a value exceeding threshold forlake eutrophication-on the year run when excluding the diffusion pollution to the lake. As a result, additional meas-ures should be taken to reduce internal phosphorus pollution even when external pollutants are under control.