| From publication of the Report of the Brundtland Commission, Our Common Future, sustainability and sustainable development have already become the main tune of worldwide development. Cities are important for word environment and resource because 'they are the site where the human impacts on the environment are most evident and the opportunities for impact reduction are most concentrated'. (White, 1994)Based on central government deploy and Shanghai's development strategy, till 2020 Shanghai needs build 'four center' and international metropolis. So Shanghai is still on speedup development phase. This basically decides that in the future 20 or 30 years large amount of immigrated population will come to Shanghai. High population growth will certainly make environmental problems, traffic problems and social problems worse. It is urgent for rban optimization.Unlike former urban optimization strategy, which is realized only by population controlling, the paper presents a new way for urban development and population controlling, that is to improve urban spatial structure. However, present theories diverge on which one is the best urban spatial structure model. What's more, city is a very complicated system and each has its own best strategy. It is also impacted by other subjects. How to build more practical development model and give decision-making suggestion? Different cities have different characteristics. Which developing model adapt to sustainable development for Chinese big cities? The paper mainly study on those problems.The paper starts with review on various viewpoints and with literature research of urban spatial convergence and diffusion and urban spatial function integration. This paper analyses former studies' shortage and try breakthroughs. First, unlike traditional economic analysis methods, from new viewpoint of microeconomic agent, the paper makes complexity simulation on sustainable urban spatial structure and gets the best spatial structure which is adaptable for Chinese big cities' development and which gives guideline for shanghai city demonstration study. Second, unlike most urban spatial studies which use common equilibrium theory analysis methods, the paper adopts the latest complexity and adaptability system theory, which makes simulation result more close realistic and comes up with more strong support for policy with technique study. The paper mainly includes two parts:First, the paper probes generally into common sense sustainable spatial structure system. Using Swarm-computer simulation platform, this part studies most non-linear micro-agents in city, which include governments, residents, manufacturers and so on, work on with each other and result in development process of urban spatial structure. The simulation compares commuter distance load, rent load and environmental load between 'centralization model', 'centralization + separation model' and 'separation model'. Based on those studies, this part comes up with generally suitable conclusion, that is: big urban spatial structure optimization relies on 'moderate scale centralization's urban structure form', 'function spatial layout-reduce commuter distance' and ' intervention influence by government public goods'. Second, using simulation result and inspiration, the paper studies Shanghai's spatial structure characteristics demonstratively:For one thing, generally speaking, Shanghai presents highly scale centralization situation in urban center. Population in high dense heartland transfers to nearby urban skirt or suburb. Immigrants mostly chose nearby urban skirt or suburb which relatively develop fast and have good condition. Comparatively speaking, net population in exurb reduces and it shows 'too sparse condition'. That is to say, immigrants and emigrants have similar choice for migrant spatial pattern, and it results in two transfer current adding. Sequence urbanization diffuses and spreads. However, this kind of urban structure as 'big city' or 'central model' or 'rolling big cake' is not good for sustainable development.For another, from the study of urban function, main function spaces, which include inhabitation, work and rest misuse, and they result in commuter distance greatly increased. Basic unit survey shows that spatial autocorrelation of employment posts density is far higher than that of density of inhabitation population. However, centralization of employment posts is freezing. It focuses on center. Main business spatial structure is also thus. So, most residents need long commuting for working and shopping. It increases greatly the load of city.Still more, from the viewpoint of government interference, Shanghai's 'One City and Nine Towns' plan, and '1966 City and Town Network' set too disperse in the second level which is new city or new town. Those two patterns are almost close to the 'separation model' in simulation. This is not good for population scope planning and collective investment planning of infrastructure construction for new town. Settlement of new town pays more attention to equation of counties, but considers little of benefits of scale economic. The function of new town of suburb is mainly inhabitation. Residents can not get integrity service such as basic employment, shopping, entertainment and so on. So they depend greatly on central city. Although, 'Three New Cities' Plan' is accorded with the concept of 'centralization + separation model' in simulation, new cities' decentralization are not effective because of unmatched infrastructure construction. Lacks of total plan and sequent objectives are also important reasons why cities and towns of Shanghai suburb can not develop quickly.The last, based on the former analysis, the paper makes clear that the aim of optimization of spatial structure in future, which is 'develop scale new city, evacuate dense central city '. The paper brings forward feasible interference measures for government on optimization of Shanghai spatial structure. First, enhance guiding role of disposition of public goods, make sequent city plan policy. Second, internalize externality of public goods deposit, reach Pareto Optimum including collect road crowd fee of central city, FAR transference, and external stakeholders of infrastructure construction in central city payback to new town for development and so on. Third, combined with improvement of social welfare, the paper suggests make ladder-like house price policy based on house area, effectively lead those high-income stratums who want to buy big area house move initiatively to suburb, support development of new town from the viewpoint of welfare economics.
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