A long history of agricultural development and the relative abundance of historical documents in the Heihe River Basin provide favorable conditions for the reconstruction of cultivated land distribution pattern changes in historical periods. According to the characteristics of land development and utilization in the Heihe River Basin in the historical period, the relationship between dominant factors which includes natural elements such as altitude, slope, and cultural elements like population distribution and cultivated land distribution is analyzed deeply. Then the factors which have a significant impact on farmland distribution and can be relatively easy to quantify are selected. Based on these factors, a set of historical farmland data grid model is established and the historical cultivated land distribution trends in the middle reaches of the Heihe River Basin before the Ming Dynasty is simulated. Using the methods of per capita cropland area and grain yield, total cropland area in the Heihe River Basin before the Ming Dynasty is estimated. Based on the grid model and combined with correcting and positioning function of ancient ruins as well as image recognition, space distribution reconstruction of cultivated land in the middle reaches of the Heihe River Basin before the Ming Dynasty is completed.