城市代谢可以厘清城市中物质、能源和废弃物的输入、流转与输出，为探寻城市环境问题产生根源提供理论基础。能值分析方法突破了能流，物流和货币流之间的壁垒，为城市代谢研究提供了新的方法和思路。本文选取北京城市系统为研究对象，对2005-2014年十年间的城市代谢进行了能值核算，将城市生态系统划分为自然、经济和社会子系统，并构建了包括能值自给率，能值货币比，人均能值使用量等的指标体系，对城市生态系统的代谢效率进行量化评价。对比分析发现，北京城市代谢不断向有益方向演进, 且具有很大的发展空间，其中自然子系统的评价结果表明北京在资源利用效率和经济发展的健康程度上有持续的提升，但环境压力很大，而且对可再生能源的利用不充分；经济和社会子系统的指标显示北京的经济发展和居民生活水平都处在一个相对高的水平，但是对电力的依赖程度有不断增强的趋势。

With the urbanization moving on, both the economy and the environment pressure are growing in a tremendous way, causing the complex among population, resources and environment continue to aggravate. Sustainable development has become the key solution to the global environment problems. The study of urban metabolism makes it possible to clarify the input, output, as well as the circulation of the material, energy and waste. The emergy analysis creatively breaks the barriers among energy flows, material flows and monetary flows, lending a new viewpoint to the study of urban metabolism. Emergy synthesis also provides a solid theory foundation of searching for the root of environment problems. In this study, an emergy accounting and evaluation of the metabolism of Beijing in a 10- year time span (2005-2014) was conducted. The index system was built on three sub systems: the natural system, the natural system, economic system and the social system, including indexes which reflect the metabolism efficiency, like emergy self-sufficiency ration (ESR), emergy money ration (EMR) and emergy use per person (EUPP) etc. According to the results in the natural system, it could be seen the increase in the efficiency of resource use. However, the environment was still under a large amount pressure, the development is still heavily depended on the support from the outside of the system and the use of renewable resources was at a limited level. Indexes in both economic and social systems were showing that Beijing has developed to be an advanced city with a relatively high living standard. But the development tended to be heavily depended on the use of electricity. If seeing from a bigger picture, the metabolism of Beijing is improving in a good direction and still holds room to improve.