| Water resources are not only the indispensable basic natural resources for supporting urban socio-economic development and ecological environment construction but also the strategic economic resources to realize urban sustainable development. With the acceleration of urbanization, urban water problems, such as water shortage, water pollution, flooding and so on, are increasingly serious, and the coordination degree between urban water resources system and urban development becomes lower and lower, which results in the prominent contradiction between water supply and demand. As a basic research subject in urban sustainable development and water security strategy, urban water resources carrying capacity (UWRCC) has caused extensive concern in the academic circles or government departments and has also become the key and hot issues in the research field of water resources science. So, it's of great significance to discuss UWRCC for urban sustainable development planning, that is, research on the ultimate limitation of the limited water supply bearing urban development elements.From the perspective of "urban water resources-social economy-ecological environment" compound system, firstly, the paper systematically and deeply studied UWRCC theory, which further perfects the systematic study on theory. Secondly, different index systems were built and appropriate quantitative models also were selected respectively from loading status evaluation and loading size prediction. Finally, aiming at evaluation process, it was successful to develop the calculation software, which can greatly simplify the operation process and real-timely obtain results to support decision analysis. Following the above research thinking, the analysis is carried out using the case city of Hefei which is a severe water-shortstage city with resource-oriented and quality-oriented dual problems, and the main achievements are obtained as follows.1. Through combing the theoretical progress of water resources carrying capacity (WRCC), the paper puts forward the scientifical definition of UWRCC, summarizes its unique connotation and characteristics, and then respectively constructs the corresponding index system from loading status evaluation and loading size prediction, all of which lay the systematic theoretical foundation for the latter research.2. From the perspective of loading status evaluation, the quantitative models of water footprint and multi-level fuzzy evaluation were selected to evaluate UWRCC in Hefei from multi directions. The results show that, the whole level of UWRCC in Hefei is "general" leaning "good", and the trend enhances gradually. Among urban water resources systems, socio-economic development system and ecological environment system, as well as within the various elements of each subsystem, the degree of equilibrium and coordination is not high with an unstable stage change. Based on these conclusions, in order to promote UWRCC in Hefei, the appropriate countermeasures are put forward, such as water resources tapping and saving, coordinated development of elements in urban compound system, regional integrated and coordinated development and so on.3. Using the improved nonlinear BP neural network modeling technology to predict UWRCC, experiment proves that it has an ideal model precision with the error absolute value less than 0.9%. According to the comparative analysis of three hypothesis scenarios, it's found that the medium prediction program of UWRCC is closer to the actual situation of the social and economic development in Hefei, which is a water-saving mode embodying sustainable development. Taking both conditions of local water supply and water diversion project from Yangtze River to Chaohu Lake into considerations, the medium prediction program tells us the largest loading population size from urban water resources is between 8.4861 and 10.2603 million and the largest loading economic scale (GDP) from urban water resources is between712.118 and 1043.771 billion yuan in 2030.4. By the mixed programming with MatrixVB and VB6.0 to develop the calculation software of UWRCC evaluation, it can realize real-time and convenient calculation analysis. In conclusion and prospect, the research deficiency is pointed out and the future research direction is also cleared.
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