Abstract: Forecasting changes in agricultural ecology is important for the maintenance of agricultural ecological security and control of agricultural ecosystem deterioration. Based on emergy analysis of agricultural ecosystem, early warning study of regional ecological security identified warning condition and the importance of agricultural ecological security, so that people can make warning and alarming as early as possible and take measures to inhibit, mitigate, control and regulate it effectively before the agricultural ecosystem degradation and qualitative change, which can make agricultural ecosystem step into a vicious cycle. In this thesis, the emergy input-output and emergy based indices of farmland in Wu’an city, Hebei province from 1997 to 2008 were studied through the emergy analysis to dynamically evaluate and identify the farmland sustainability. The early warning system of Wu’an farmland with Grey Model was established for early warning of farmland use. The results indicated that Wu’an city Hebei province had more reliannce on the local non-renewable resources input, more environmental pressure and lower sustainability. It changed from no warning condition in 1997 to warning condition in 2008, and it would be consistent in warning condition in 2015, 2020 with Grey Model. In addition, the index of agricultural ecological security of each town is presented. Meanwhile, the countermeasures of sustainable agricultural development are pointed out, which can provide a basis and example for ecological regulation and control of sustainable agricultural development.