Abstract: The spatial variation and cause of phosphorus fractions in sediment of Western Taihu Lake were examined by the Standards, Measurements, and Testing Program(SMT) method.The results show that all the phosphorus fractions declined with depth, which reveals the enrichment effect of phosphorus pollution in surface sediment. Space diversity of total phosphorus(TP) and phosphorus fractions in sediment of sampling sites observed in Western Taihu Lake. With the reducing of phosphorus pollution, the phosphorus content in water has been decreasing slowly in surface of southwestern area of the lake. The phosphorus pollution levels of the northwest area of the lake were higher than those in southwest areas in the sediments, which is related to the impact of prevailing wind direction, geographical location and surrounding ecosystem condition. The TP content in the lake ranged from 337.27 to 1 081.87 mg·kg^-1 and inorganic phosphorus(IP) was the main component of TP in sediments, accounting for 55.27% to 97.93% of TP. IP was dominated by the hydrochloric acid extractable phosphorus(Ca-P) in sediments, accounting for 44.14% to 89.30% of IP. Significantly correlations are existing between TP and IP, and IP and Ca-P, which show that TP content is mainly affected by IP content, and IP content is affected by Ca-P content. The correlation between TP and Fe/Al-P was also significant, which reveals that the external pollution caused by human activities is the major source of phosphorus pollution in sediment.