Abstract: Mesozoic granites in the Xiao Qinling Mountains are represented by a complex pluton consisting of the Laoniushan, Huashan and Minyu granite bodies. Within the complex pluton there occur many types of lithologic zones, indicating that the pluton has an evolutionary regularity of polyphase meltingdifferentiation and emplacement and a sequence of compositional and structural evolution. Through studies of the lithology, composition, textures and structures, contact relationships and temporalspatial distribution of the rocks, the authors make lithodemic division of the rocks and establish the Huashan superunit assemblage. They propose that the essential rock sequence is the basic unit for observation and description in geological mapping in the area of magmatic rocks as well as the basis for lithodemic division.