Abstract: The water and sediment phosphorus forms in small watershed are diverse and the influencing factors are complex, which is one of the challenges in the study of watershed water environment. Through field sampling, experimental processing and data analysis of Xiaodong River, this study aims to reveal the spatial and temporal distribution characteristics and influencing factors of phosphorus form in water and sediment of the basin during dry season and rainy season, and explore the relationship between water environment index and phosphorus form. The results showed that there was a significant difference in total phosphorus between the dry season and the rainy season (P < 0.01). In the dry season, total phosphorus gradually decreased from upstream to downstream, while in the rainy season, it was the opposite. Granular phosphorus accounted for 70.8% of total phosphorus concentration in dry season and 68.9% in rainy season. The total phosphorus in sediments increased gradually from the upper reaches to the lower reaches, and the phosphorus form in sediments was dominated by Fe-Al combined inorganic phosphorus. Redundancy analysis showed that water temperature and total nitrogen greatly influenced the phosphorus morphology in water and sediment in dry season, while dissolved oxygen, chemical oxygen demand and temperature influenced the phosphorus forms in rainy season. Spearman correlation analysis further revealed that there was a significant correlation between water phosphorus and sediment endogenous phosphorus in the dry season (P < 0.05), and the endogenous influence was less in the rainy season, and phosphorus in the rainy season may mainly come from the input of rainfall runoff (including agricultural non-point source material, urban domestic sewage overflow and rural domestic sewage, etc.). The research provides important theoretical support for the water environment management of Xiaodongjiang River.