Northern region wheat and corn were taken as the research main bodies, and the field of Da Xinfeng village in Cuicun Town, Changping District, Beijing was taken as an example, the parameters of precision fertilization decision-making system was researched and corresponding mathematical model was established, the algorithm model and the database were unified, linear regression method to calculate fertilizer needed like N, P, K of soil was used. Two-dimensional interpolation method was applied to calculate unknown point of the region with the test samples in the region, thus soil fertility information database was established. Through the above ways and combined with the soil nutrient, crops type and the target yield and so on, the fertilizer needed of the region was determined, which could provide theory basis for circulation agriculture. 