West Lake in Hangzhou is a small shallow lake. Its surficial sedimentary stratum is composed of algae faulschlamm layer and peat layer, and is mainly characterized by high organic carbon content and extreme high nitrogen contents but by relatively low degree of phosphorus enrichment. A simulation study in laboratory and on the spot was conducted to determine the effects of various environmental parameters on the phosphorus release rate and the capacity from the sediments of West Lake in Hangzhou. Factors investigated in laboratory included pH, temperaturetdissolved oxygen, redox potential and overlying water type. The lowest release capacity was found when the pH was at the range of 6.5-7.0 for the overlying water. Raising the temperature or lowering oxygen concentrations in the overlying water may also accederate phosphorus release. The highest release capacity was found to be about 0.368 μg P/g in laboratory. The average release rate measured on the spot in summer was 1.02 mg P/m²·d. The calculated release capacity from the sediments of West Lake was 1.346tP/a, equivalent to 36.4% of the average annual external phosphorus loading. The internal loading is a major contributory factor in the continuing eutrophic states of the lake.