[Objective] In order to provide basic data for the prevention of agricultural nonpoint source pollution and the protection of water resources in the Three Gorges Reservoir area, the phosphorus loss in regular lime slope farmland under different gradient was researched.[Methods] A sloping farmland in Xiangxi watershed of Three Gorges Reservoir area was selected and an artificial rainfall experiment with rainfall intensity of 1.5 mm/min was conducted. The variations in surface runoff, sediment concentration, total phosphorus(TP) concentration and other forms of inorganic phosphorus were studied.[Results] As the increase of slope, total runoff and sediment increased, whereas, the initial runoff time decreased. However, no significant impact on the sediment concentration was observed. As runoff continued, both TP and particulate phosphorus(PP) decreased and reached a steady concentration under all slope gradients. PP was the primary form of phosphorus loss, accounting for over 80% of that. The inorganic phosphorus suffered the most severe loss for the phosphorus loss of sediment. The inorganic phosphorus grading tests showed that effective phosphorus and slowly available phosphorus accounted for 54.1%~57.8% of the total amount of inorganic phosphorus.[Conclusion] Slope gradient influenced the phosphorus loss through the impacts on surface runoff and sediment loss. The phosphorus of sloping farmland of limestone soil was mainly removed with the sediment.