Abstract: In order to calculate rationally farmland potential productivity and fully utilize the results of agricultural land classification, the farmland grain potential productivity system was put forward. The method to calculate grain potential productivity at different levels was discussed. Grain potential productivity system includes natural potential productivity, utilization potential productivity and actual capacity. The natural quality index and the utilization quality index are intrinsically two different kinds of grain potential productivity. They respectively stand for two kinds of potential yield per unit area. Hence, the corresponding potential productivity of a unit of agriculture land classification is the unit area times its corresponding quality index. The grain corresponding potential productivity of the whole county is the sum of the potential productivity of all units. Based on the theoretical analysis and modeling using many models, the results indicate that it is better for the actual productivity calculation to use Logistic model. The results show that the natural potential productivity of farmland of Zhouzhi is 176.778×104 t, the utilization potential productivity of farmland of Zhouzhi is 105.0×104 t, and that the actual capacity of Zhouzhi is 54.637×104 t.