Abstract: Thematic attribute data is one of the most important components of GIS.With the development of GIS application in more and more fields,the professional GISs are built with the combination of GIS and professional data.These professional data is the important contents of thematic attribute data.Therefore,an urgent problem is to develop a set of comprehensive methods and systems of thematic data generalization.The subject of the paper is to discuss some key problems of thematic data generalization in GIS:to analyse the relationship between thematic data generalization and spatial data generalization,to consider two models about the implementation of thematic data generalization in GIS and to discuss the basic routine of the implementation of thematic data generalization.