The efficiency of sediment capping with an alum sludge to prevent phosphorus release from surface sediment of reservoir under anaerobic condition was investigated through a incubation experiments, Incubation experiments proved that the T-P from the sediment into the overlying water under anaerobic condition was significantly reduced by the alum sludge, And, during the adsorption of T-P, the reduction in T-P concentration occurred with increase in concentration of T-N, TOC, sulfate and chloride. The extraction amount of T-N, TOC, sulfate and chloride from the alum sludge for 3Odays were O.009 (T-N), 0.1 0(TOC), 1 .38(sulfate) and 0.08 g/kg sludge (chloride), respectively, However, there was no significant release of aluminium during the adsorption of T-P. And T-P removal efficiency increased from 60 to 100% when alum sludge dosage was increased from 12 to 48g alum sludge/kg sediment. At dosage 48 g alum sludge/kg sediment, the uptake of T-P was 0.014 g/kg sludge. It was amount in 2% of the maximum adsorption capacity for phosphorus in alum sludge. It is suggested that the alum sludge can further be used as a capping material of T-P adsorption in reservoir.