Abstract:Policy decisions associated with urban development are usually made with a flowed accounting system that ignores the basic life-support system for all metabolism activities. Studying urban life-support system and analyzing its biophysical base systematically of urban ecosystem is a new perspective to understand the mechanism on modern urban illness. Emergy method, one of ecological energetic method, was adopted to analyze the urban ecological economic systems. The relevant indices and ratios based on emergy flows can be used to evaluate the behavior of ecological economic systems, for the present case, however, a new indicator of Urban Ecological Competition Capacity Index (UECCI) was put forward based on available emergy indicators to assess the overall performance of urban ecosystem. Beijing, Shanghai and Guangzhou were chosen as case cities and the period from 1990 to 2005 was considered. Meanwhile, previous evaluation results of Taipei in 1991 and 1998, and Macao in 1990, 1993, 1995, 1997, 2000, 2003 and 2004 were also incorporated for cross references. The results show that the evolution trends for three cities appear to be very similar, however, the UECCI of Guangzhou is higher than those of Beijing and Shanghai, and thus it seem to have greater ecological competition capability from the perspective of longer term sustainability. Further comparison with Taipei and Macao, it is found that the development level of mega cities in mainland are inferior to those of Taipei and Macao to some extent, but the UECCI of case cities are higher than those of Taipei and Macao.