Abstract: The alfalfa growing for 1, 2, 3, 4 and 6 years on experimental farm of Inner Mongolia University for Nationalities were used to study the yield variation and the content of N, P and K in soil. The results showed that the yield decreased along with the growth year and the yield in second year was the highest. The content of total N, available N and P increased along with the growth year. The total P increased at the beginning and then decreased, available K and total K decreased. Nutrient contents within 0 to 40 cm soil layer decreased as the depth increasing. The nutrient contents within 40 to 50cm soil layer were higher than those in 30 to 40 cm layer.