In order to explore the response of switchgrass (Panicum Vigatum L.) to phosphorus supply level under saline-alkali conditions，different varieties of switchgrass (three species，Alamo diploid，Alamo，Pathfinder) were used as materials for root box test，the root morphology and physiological characteristics of switchgrass and soil physicochemical properties treated with different phosphorus concentrations (0，10，100 mg/kg) were analyzed and compared.The results showed that with the increase of phosphorus application level，the biomass，root morphology，root activity and soil available phosphorus content of all switchgrass varieties showed an overall upward trend，while the root-shoot ratio，soil pH value and acid phosphatase activity showed a downward trend，all of which reached the maximum and minimum values under the treatment of high phosphorus (100 mg/kg).Compared with high phosphorus treatment，under low phosphorus (10 mg/kg) treatment，the soil pH value of three switchgrass varieties increased by 0.31，0.28 and 0.23 units，and the acid phosphatase activity increased by 58.0%，42.0% and 13.5% on average，respectively.Under the condition of low phosphorus，Alamo diploid has a large root surface area，maintains high root activity，and shows strong adaptability，which is conducive to lowering soil pH and improving soil acid phosphatase activity.Generally speaking，the adaptability of Alamo diploid to low phosphorus stress in saline-alkali soil is better than Alamo and Pathfinder.At the same time，increasing the phosphorus supply level can promote the root growth of switchgrass in saline-alkali soil，improve the soil environment and increase its biomass output.