Abstract: Symbol library is one organic component of Geographic Information System(GIS). Development of flexible and applicable symbol library is one important task to programming GIS software. The accuracy of output map of GIS is related to the symbol library. How to develop scientific symbol library is the domain of this artical. The basic concept and hierarchical structure and main function of symbol library are discussed at first. Then the classification system of map symbols is set up according to characteristic of symbols and handling manner of symbol library. While the "Symbol Set" term is used to discusse the creation of symbol library contents, many kinds of operations of symbol library are studied by use of "Operation Function". Finally, the authors take the National Symbol Library of Coal Field Geology and Symbol Library of Coal Mine Geoglogy and Survey as examples to introduce the development and application of symbol library.