[Objective] Soil microbial biomass (SMB) is a pool of soil available nutrients, directly participating in the transformation and biogeochemical cycling of soil carbon (C), nitrogen (N), phosphorus(P)and sulphur (S). Soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), and soil microbial biomass phosphorus (SMBP)are main components of the SMB, which serves as a hub for material cycling in the pedosphere. Since SMB is sensitive to environmental conditions, any change in SMB will affect turnover of soil elements. Therefore, SMB is considered to be a sensitive and effective indicator of soil fertility and biological quality. The study on rules of spatial distribution of SMB pool is of important significance to grasp how soil nutrients recycle in situ and how to manage soil nutrients regionally.[Method] In the present study, to explore how SMBC, SMBN and SMBP distribute spatially and what their influential factors are in the farmland ecosystem. A soil survey was conducted in Quzhou County, a typical agricultural county in the North China Plain with 56 740 hm² of farmlands. Using the grid sampling (2.5 km×2.5 km) method, soil samples were collected from the topsoil layer (0-30 cm) of a tract of farmland for analysis of spatial distributions of SMBC, SMBN and SMBP pool with the geostatistical method.[Result] Results show:(1) The average reserve of the SMBC, SMBN and SMBP pool was 64.14×10³ t, 24.55×10³ t and 2.8×10³ t, respectively, in the topsoil (0-30 cm) layer of Quzhou County. SMB was distributed in patch, featuring moderate spatial variability and obvious spatial autocorrelation; (2) Crop yield was significantly and positively related to MBC and MBN; (3) The mean content of carbon, nitrogen and phosphorus in soil microbial biomass per unit weight varied sharply with planting system, being higher in the wheat/maize rotation system than in the cotton monocropping system, which indicates that rotation system is superior to monocropping system to some extent, and favorable to maintaining a large soil microbial biomass pool; (4) Size and spatial distribution of SMB pools were governed by planting systems and soil fertility. MBC, MBN and MBP were closely related to soil fertility (e.g., soil organic carbon, total nitrogen, available phosphorus, available kalium), among which soil organic carbon is the most important factor.[Conclusion] For the first time, sizes of SMBC, SMBN and SMBP pools were quantified, and spatial distribution pattern and influential factors of SMB were specified in the farmland of the North China Plain. In the farmland soil of Quzhou County, soil organic carbon is the most important factor affecting SMB pool, which suggests that soil microorganisms are limited by C. Therefore, it is advisable to strengthen application of organic manure, return straw to the field and reduce mineral fertilizer application rate so as to regulate and utilize the SMB pool in the future. All the findings in this study indicate that soil microbial biomass is a potential available nutrient pool in farmland in North China and may serve as a scientific basis for regionalized nutrient management and precise agriculture.