In order to study the effects of microbial fertilizer and mixedsowing on soil enzyme activities and microbial biomass，eight treatments were set up as follows: Alfalfa sowing(N1),Feed sorghum sowing(N2),Alfalfa mixedsowing with feed sorghum in the same row(N3),Alfalfa mixedsowing with Feed sorghum in different rows(N4) and each applied with microbial fertilizer(T1,T2,T3 and T4).Soil samples in the soil profile of 0~20 cm，20~40 cm and 40~60 cm were taken during seedling period，strong period and harvest period.And the soil urease，invertase，catalase activity and microbial biomass carbon and nitrogen were measured.The results showed that soil enzyme activities and microbial biomass were significantly higher than those of nonapplied with microbial fertilizer and unicast forage treatments respectively，and the treatments of mixedsowing combined with microbial fertilizer were the best.The activities of soil enzymes decreased gradually with soil depth.The activities of catalase and sucrase decreased firstly and then increased with the growth of forage.The activity of soil urease increased firstly and then decreased.The laws of microbial biomass C and N were the same with urease.Mixedsowing with microbial fertilizer is beneficial to increase enzyme activity and soil microbial biomass，and enhance the sustainability of soil productivity so as to achieve the effect of protecting and improving the soil environment，provide rotation crop for potatoes in Inner Mongolia and provide sufficient forage，and all these are of great significance to the development of agriculture and animal husbandry.