Abstract: Urban ecosystem is an economicsocialenvironmental comprehensive system. It is important to discuss the inner interaction within the system to perform sustainable development strategy. In this paper, the theory of carrying capacity is reviewed and extended to the urban ecosystem. From the view of carrying capacity, we advanced the concept of carrying relationship: sociometric activity is the driving factor, while ecological environment is passive; the interface relationship between them is the press are and carrying relationship which is named as carrying relationship of urban ecosystem. Then two concept models which are the carrying hierarchy and watering bucket model are used to describe the carrying relationship of urban ecosystem. An evaluation model, involving 35 indicators, is set up and a series of indexes, such as resource carrying index (RCI), environment limited index (ELI) and comprehensive carrying index (CCI) is introduced to describe the carrying relationship of urban ecosystem. At last, an evaluation on the eight representative cities in Changjiang delta is carried out from the view of carrying relationship, and the result indicated that the sequence of the comprehensive carrying index (CCI))from the high to low is Shanghai, Nanjing, Wuxi, Ningbo, Hangzhou, Suzhou, Changzhou, Yangzhou.

Key words: urban ecosystem, carrying relationship, carry hierarchy model, watering bucket model, Changjiang delta