Urban land structure, layout, and land-use mode influence regional sustainable development greatly. However, planners usually cannot work perfectly because of insufficient environmental information for decision making. In recent years, with urban geographic information system (GIS) development many cities have already built up integrated urban information platform to support regional digitalization process. By using spatial data mining technology urban planning related knowledge can be discovered form GIS database to help planners and decision makers in their work. Through analyzing of Chinese cities’ construction mode and developing trend, this paper illustrates how to build up an urban planning spatial decision support system (UPSDSS) based on exploratory spatial data analysis technology support. By spatial data mining form GIS database, UPSDSS can provide related knowledge for urban planning decision making with inference engines (rule inference and case inference) support. As an important part of the research, UPSDSS had been used in urban planning management of Harbin city in China. With hidden information discovered by UPSDSS Harbin planners work easily and effectively. Three cases demonstrate how UPSDSS helped Harbin city in policy making in macroscopic urban expending planning, underground exploitation scheme making, and local land structure changing. [ABSTRACT FROM AUTHOR]