Chemical forms of phosphorus in the water and sediments from Pengxi River in the Three Gorges Reservoir were investigated from Jan 2015 to May 2015.The results showed that the content of total phosphorus,dissolved total phosphorus and soluble reactive phosphorus was 0.066-0.129 mg/L,0.033-0.118 mg/L and 0.013-0.094 mg/L,respectively.All three chemical forms and their relative ratio varified spatially and temporally.The concentration of dissolved total phosphorus and soluble reactive phosphorus was negatively correlated with the concentration of Chla.The total phosphorus in the sediments was 0.6-1.0 mg/g.The value was close to the content in sediment from Yangtze River (Wanzhou region) and smaller than that in soils from Pengxi River.The phosphorus concentration in sediment samples from Shuangjiang Bridge profile was higher than that of the other three profiles because of human activity.The result of SMT sequential extraction analysis showed that inorganic phosphorus was the main chemical form of phosphorus.Apatite phosphorus was the second predominant species while organic phosphorus and non-apatite phosphorus were the minor compositions.The ratio of non-apatite phosphorus to total phosphorus in the sediments from upper profile (Quma,Gaoyang) was higher than that from downstream (Shuangjiang Bridge).Since the bioavailability of non-apatite phosphorus was higher than that of the other two chemical forms,the contribution of phosphorus from sediment,especially from upstream sediment,to the growth of aquatic organism like alga etc.could not be neglected.