For preventing farmland degenerating and increasing food production, this research used some theories and practices of early-warning both in home and overseas for reference. This paper collects and processes datum, designes technical flow and system structure, builds index system, chooses the early-warning models, and implements system function. Finally, the cultivated land quality early-warning system was proposed based on WebGIS. Using Feidong as an example, cultivated land capability class was established and cultivated land fertility was predicted.