Abstract: Farmland has been divided into many smaller blocks, and scattered distribution, so a fertilization decision support system based on land plots is favorable and necessary in China. In this study, a fertilization decision support system was developed based on the long term field experiments in black soil region, northeast China, 723 land plots charged by farming household were taken as fertilization units, and the expert knowledge base was established according to the long term field experiments and soil nutrients balance models. The 500 soil samples with 0-20 cm layer were collected from the crop field with area of 450 ha at Guangrong Village, Hailun County; the soil map, landuse map and 723 land plots map contracted in households also were collected and treated by using ArcGIS. The database was established by the collecting data and farmland fertility survey. The geostatistics and Kriging methods were used in order to analysis the spatial heterogeneity of available nitrogen (AN), available phosphorus (AP) and available potassium (AK) and build soil nutrients maps, and then, the map of fertilization units was built mainly concerned with these soil nutrients. The VB script was used to develop the system on Super Map GIS platform. Using this system, decision makers could know the spatial variability of soil fertility and make decision on soil fertility and crop planting strategy; and farmers could access the system to obtain fertilizer recommendations for each field easily. This research will be very useful to promote the application of agricultural information through GIS.