As economies and ecological support system become more interdependent, new disciplines are needed to "bridge the gap"of understanding between societies and nature. It is now clear that neither ecology nor economics alone can address the problems of our global commons. New measures of wealth, of value, of contributions and production are needed that acknowledge the "natural capital" and "ecosystem services" provided from healthy environments. In order to study and view eco- economic system from a new visual angle, new tools are being invested to measure wealth, services and production fairly and equitably. Systems analysis approach is powerful to study the combined eco- economic systems of many scales. Diagramming is done with energy system symbols. The symbols each have rigorous energetic and mathematical meanings. We use an alternative measure of value, based on real contributions to system performance, termed "emergy". It is a concept which quantifies "energy memory"in products and processes. It is a new accounting unit of total contributions, direct and indirect, used in generation of a product or service. This broader approach could help us to investigate resource utilization and potentionalities and exchange in eco- conomic systems. Emergy analysis allows comparison and incorporation of environmental costs and benefits to provide a more comprehensive perspective for public policy directives. An emergy analysis of Miyun system of economy and nature was performed in order to study its sustainability and emergy use. Indices of thermodynamic and economic vitality of Miyun were evaluated and a comparison with indices of other developed and developing areas was performed. The results show that in Miyun County the total emergy use in 2003 was 2.49 ×10²¹sej, which was worth of 6.55 ×10⁸US$ , and the emergy- dollar ratio was 2.99×10¹²sej /$, lower than the average emergy- dollar ratio of China. The emergy use per capita is 5.885.88×10¹⁵ sej/person/a, much lower than that of Beijing (17.89×10¹⁵sej/person/a). The developed carrying capacity of population is about 51 ×10⁴ persons. At present, the population reaches 42 ×10⁴, so it is important to make right policies to control population. The emergybased sustainability index was 0.52, which means the economic increase is based on large resource consumption, so enhancing the resource utilization efficiency and establishing rational industry structures are very important for sustainable development in future.