The effect of Melilotus officinalia on improving degraded soil is studied according to the change in nutrient content of soil after planting. The results show that planting Melilotus officinalia can increase soil organic matter，total N，hydrolytic N，total P，and available K significantly，but decrease available P and total K.The reason for the latter decreases is that Melilotus officinalia needs phosphate fertilizer and potassium fertilizer to satisfy its growth.Therefore，during the growth of Melilottts officinalra，phosphate fertilizer and potassium fertilizer should be applied reasonably in order to boost nitrogen levels in the soil.This biotechnology technique functions to improve saline alkaline soil and increase the fertility of soil.The experiment indicates that Melilotus officinalia is an excellent kind of pasturage for improving the degraded soil in arid and semiarid regions.