Abstract: In order to understand the biological improvement effects,we planted 5 plant species including Frumentacea,Sesbania,Sudan-grass,sweet clover and oat in moderate and severe salinized soil of Hetao irrigation area,Inner Mongolia.The results showed that,compared with the control,all plant species significantly reduced soil bulk density and increased soil porosity.The soil bulk density with Sesbania,Frumentacea and Sudan-grass treatments decreased by 4.1%,3.4% and 4.1%,the total soil porosity with Sesbania,Frumentacea and Sudan-grass treatments increased by 5.9%,4.0% and 3.8%,and capillary porosity with Sesbania,Frumentacea and Sudan-grass treatments increased by 7.1%,5.9% and 4.2%,respectively.All plant species effectively reduced soil salinization and improved soil fertility.Soil total salt and alkalinity with Sesbania,Sudan-grass and Frumentacea in plough layer decreased significantly; the total soil salt decreased by 15.8%,18.8% and 15.0%,while the alkalinity decreased by 28.6%,28.6% and 26.1%,respectively.Sesbania mostly improved soil organic matter,total nitrogen,available nitrogen,available phosphorus and available potassium by 65.4%,68.4%,43.9%,43.6% and 36.4%,respectively.The effect of 5 plant species on salinized soil improvement was in an order of Sesbania> Sudan-grass >Frumentacea>Sweetclover> oat.Planting Sesbania mainly,supplemented by Frumentacea and Sudan-grass,are encouraged in the moderately and severely salinized area.