Study on the distribution, influencing factors, and pollution risk of phosphorus forms in karst canyon reservoir sediments is highly concerned in water pollution control and aquatic ecosystem management. The study selected a typical karst canyon reservoir (Wanfeng Reservoir) as the study area. By analyzing the distribution of sediment phosphorus forms, this study identified the influencing factors of the spatial variation of sediment phosphorus forms, and assessed phosphorus pollution. The results showed that (1) the total phosphorus (TP) content in sediments had a range from 79.37 to 438.04 mg/kg, with inorganic phosphorus (IP) accounting for 73.26% to 78.84% of the total. IP was the dominant form of phosphorus in sediments. The content of iron-aluminum-bound inorganic phosphorus (Fe/Al-Pi) was 16.86 to 91.82 mg/kg, which was the dominant form of IP. Weakly adsorbed organic phosphorus (H₂O-Po) with a content of 0.27 to 8.03 mg/kg was the dominant form of organic phosphorus (OP). (2) Residual phosphorus (Res-P), weakly adsorbed inorganic phosphorus (H₂O-Pi), calcium-bound inorganic phosphorus (Ca-Pi), potential active inorganic phosphorus (NaHCO₃-Pi), and iron-aluminum-bound inorganic phosphorus (Fe/Al-Pi) were the main influencing factors causing the spatial variation of TP. The sediment depth had multiple impacts on TP, and significantly influenced by the interaction with other factors. (3) Bioavailable phosphorus (BAP) had a range from 66.97 to 201.46 mg/kg, accounting for 55.6% to 59.6% of total phosphorus. The mean value of phosphorus pollution index and bioavailability index were 0.53 and 0.81, respectively. This indicated that the overall degree of phosphorus pollution in sediments was mild, implying certain pollution risk to the overlying water. In addition to controlling external phosphorus loading, managing sediment phosphorus is also recommended for karst canyon reservoirs to reduce sediment phosphorus release and pollution to the overlying water.