Raster is used widely as a basic object in the geography information science

because products producted by raster have real spatial size and many math models are more easily built based on raster. Fuzzy comprehensive assessment is applied widely in the field of multi-factors evaluation application. Sometimes spatial data and spatial concept are fuzzy in geography information science

so fuzzy spatial analysis has gained more and more attention from researchers during the recent years

but fuzzy comprehensive assessment method is used rarely in multl-raster data. The theory of fuzzy comprehensive assessment is described in detail firstly. Then the GIS model about fuzzy comprehensive assessment is built based on multiraster data and spatial overlay analysis. The GIS model has been used in the urban air quality assessment successfully. The result of the instance shows that this model can well conduct fuzzy comprehensive assessment based multl-raster data.