Abstract: In order to investigate the effect of different years of fallowed farmland on soil microbial characteristics, different ages of fallowed farmland (1, 2, 3, 5, 8, 15, 24, 31 a) in Minqin Oasis were used for the study. The spatial scale instead of the temporal scale was used to study the characteristics of soil microbial biomass and its seasonal dynamics in the secondary grassland of Minqin Oasis for different years (1-31 a). The results show that (1) soil microorganisms were higher in the surface layer than in the deep layers of the secondary grassland in the same years of fallowing, The highest soil microbial carbon content of the surface layer was 979.13 mg·kg^-1, while the highest soil microbial carbon content was 610, 480 and 327.74 mg·kg^-1 with the soil depth of 10-20, > 20-30 and > 30-40 cm, respectively, accounting for 62%, 49%, 33% of the contents in the surface layer, respectively. Soil microbial biomass nitrogen and soil microbial biomass phosphorus had the same results, indicating that the soil microbial biomass clustering was obvious; (2) soil microbial biomass carbon and microbial biomass nitrogen generally showed a fluctuating decrease with the increase of fallowing years, and soil microbial biomass phosphorus showed a trend of undulating increase with the increase of fallowing years; (3) the dynamic change of soil microbial biomass carbon content with different seasons was obvious, with the minimum in winter, the maximum in autumn, and the medium in summer and spring, and the range of soil microbial biomass carbon content in the surface layer (0-10 cm) was large; (4) the seasonal dynamics of microbial biomass nitrogen showed an inverted V-shaped distribution, and the dynamic change of it was the same as that of microbial biomass carbon. (5) the seasonal dynamics of soil microbial biomass phosphorus content were larger in autumn and summer, intermediate in spring and minimal in winter. From March onwards, soil microbial biomass phosphorus gradually increased as the month increases, reaching a peak in June or September, and then decreased continuously, falling to a minimum in December. (6) According to the research, it can be concluded that the first five years was the key period for the restoration process of fallowed farmland in Minqin Oasis.