In order to study the effects of combination of super absorbent polymer and microbial fertilizer on soil microbial biomass carbon, nitrogen and enzymes activities, four treatments, including no application of super absorbent polymer and microbial fertilizer (CK), combination of super absorbent polymer and microbial fertilizer (A), single application of microbial fertilizer (B) and single application of super absorbent polymer (C) were set up in the dryland area of the Loess Plateau. The spatial and temporal dynamics of soil microbial biomass carbon, nitrogen and enzymes activities of 0-10, 10-20, 20-40 cm soil layers during oat growth was analysed. The results showed that: (1) During the whole growth period, soil microbial biomass carbon showed a double-peak curve, the peaks appeared at the booting and filling stages. The soil microbial biomass nitrogen showed the trend of first decreasing, next increasing and then decreasing, with the highest content at the seeding stage. All the soil catalase, invertase and urease activities showed a single-peak curve, with the peak activities of soil catalase and invertase at the booting stage, and the peak of soil urease at heading stage. (2) Except CK, all the soil microbial biomass carbon, nitrogen, soil catalase, invertase and urease activities showed 0-20 cm > 0-10 cm > 20-40 cm. The combination treatment (A) had significant effects on 0-10, 10-20 cm soil layer (p<0.05), the single treatments (B, C) had significant effects only on 10-20 cm soil layers (p<0.05). (3) In 10-20 cm soil layer, compared with other three treatments, the combination treatment (A) all had the significant effects (p<0.05). Soil microbial biomass carbon was improved by 4.82%~40.28%, soil microbial biomass nitrogen improved by 8.44%~68.66%, soil catalase activity improved by 13.32%~60.16%, invertase activity improved by 10.45%~39.14% and urease activity improved by 12.40%~55.62%. (4) Combination treatment (A) had significant effects both on grain and biological yield (p<0.05), the increasing range was 8.40%~20.12% and 10.80%~25.09%. So the combination of super absorbent polymer and microbial fertilizer had best effects on improving soil microbial activity and oat yield in the dry farmland of Inner Mongolia Loess Plateau.