Abstract: In order to reveal the ecological functions of riparian zones in different watersheds, the soils in different riparian zones (woodland, cropland, grassland and wasteland) of Tiaoxi watershed and Tianmu Lake watershed in western Taihu Basin were collected and analyzed in the summer of 2015. Phosphorus fractions were obtained by a sequential extraction procedure. Spatial distributions of phosphorus fractions in soil profiles, influence factors and the relationships between phosphorus fractions in soils and the total dissolved phosphorus (TDP) in ground water were analyzed. The results showed that phosphorus fractions concentrations of riparian soils in Tiaoxi watershed were higher than those in Tianmu Lake watershed, but there were differences in compositions. Generally the loosely absorbed phosphorus (NH₄Cl-P), reductant phosphorous (BD-P) and metal oxide bound phosphorus (NaOH-P) concentrations decreased with the increase of soil depth, while calcium bound phosphorus (HCl-P) concentrations increased with the increase of soil depth, and cropland showed the most obvious tendency in vertical direction. From upland to waterfront, phosphorus fractions concentrations in soils of grassland and wasteland profiles increased slightly, while those of woodland and cropland profiles decreased. Cropland also showed the most obvious tendency in horizontal direction. Overall, the horizontal changes of phosphorus fractions concentrations of soil profiles of Tiaoxi watershed were more obvious than those of Tianmu Lake watershed. The correlation analyses showed that NaOH-P contributed more to TDP in the ground water. Organic matter, clay mineral and carbonate showed stronger effects on phosphorus fractions than other soil properties. Phosphorus fractions in riparian soils of Tiaoxi watershed had weak relationships with the soil properties, while those of Tianmu Lake watershed had strong relationships with the soil properties. Therefore, there were differences in spatial distributions of phosphorus fractions in different riparian soils in Tiaoxi and Tianmu Lake watersheds and their influence factors were also different. There was a significant relationship between phosphorus fractions in soils and TDP in the ground water, especially NaOH-P.