Abstract: Whether the regional farmland ecosystem with high yield is sustainable or not is a key issue concerned food security. Based on the methods of emergy analysis and household questionnaire investigation, this paper studied the changes of the total amount of emergy input and output, the structure of emergy input and output and the comprehensive indexes of sustainable development from 1996 to 2006 in Huantai County with high yield in North China. The results showed that during the last 10 years, the total amount of emergy input rised by 26.50% while total amount of emergy output only rised by 5.71% per hectare; from the perspective of the structure of emergy, the farmland ecosystem used less organic energy and more natural resources and industrial energy; according to the comprehensive indexes of sustainable development, the environmental load ratio was increased that showed the environment carried more pressure; the emergy yield ratio was decreased; the emergy sustainable index was decreased which showed that the sustainability of farmland ecosystem in Huantai County was reduced.