The real world is an infinite complex and very huge systems, the phenomenon and processes in this world have many complex relations among them. It is consecutive and cannot be treated as a determined one as the traditional geographic information system does; What's more, the uncertainty and fuzziness exist in every stage of data processing of GIS, from data collection, data storage to data analysis etc, so it is very meaningful to apply fuzzy theory in GIS for its ability to handle fuzziness and uncertainty of spatial data. The paper talks about the current situation of fuzzy theory applied in
GIS, including the classification of application fields, its main methods, principles etc. The detailed fields we concerned include spatial object modeling, spatial reasoning, spatial analysis, spatial data mining, and reliability analysis of GIS data and so on. Furthermore, we put forward some development foregrounds and research orientations of fuzzy theory applied in GIS.