The urban ecosystem is composed of natural and socioeconomic subsystems. its direction of evolution is often determined by the economic value and benefits of the system's outputs, which however cannot fully describe the flows of substances, energy, information and population. Based on dissipative structure theory and urban nature-economy-society complex ecosystem theory, an indicator system and a model based on information entropy, which can measure the various flows in an urban ecosystem, are developed for evaluating the direction of change in urban development. in addition, the year- and indicator-based information entropies were estimated for the urban ecosystem. In total, four types of information entropy, including sustaining input, imposed output, destructive metabolism and regenerative metabolism, were calculated by using year-based information entropy to analyse the order and complexity of the urban ecosystem; the weights of indicators were calculated, and index scores for the urban ecosystem were calculated by using standardized values of the indicators. The values of index for sustainable development helped to identify the developmental level and harmonious degree of the urban ecosystem. By using these methods, the progress of sustainable development of Ningbo City (China) was evaluated from 1996 to 2003. The results showed that the order degree of Ningbo's urban ecosystem is increasing, the urban ecosystem's service function is improving and the health level of the system is strengthening. The developmental degree and the harmonious degree of the system's entropy flow increased from 1996 to 2003, and underwent a complicated transformation from a situation in which socioeconomic pressure dominated towards a situation in which the ecological carrying capacity became more adequate. The developmental degree of entropy production by the system first increased and then decreased from 1996 to 2003, leading to instability of the system's metabolism function. Its harmonious degree changed irregularly from 1996 to 2003, and underwent a complicated course from destructive metabolism to regenerative metabolism, then returned to destructive metabolism. (c) 2006 Elsevier B.V. All rights reserved.
