Abstract:The region bordering on Hunan, Guizhou and Guangxi Provinccs (HGG) is located in southwest of Hunan, southeast of Guizhou, north and northeast of Guangxi at latitude from 24° 37＇ to 26° 40＇N and longitude from 107° 52＇ to 111° 34＇ E, covering a total area of 70418 km2. Quantitative studics on thc relationship between the HGG flora and the neighbouring floras were made. The results showed that the similarity coeffcients of spermatophyte floras between HGG and neighbouring floras were in order from high to low: Nanling, C. China, E. China, YGG (region bordering on Yunnan, Guizhou andGuangxi Provinces), and Lingnan (south area from the Nanling Mountain) at family level, and E. China, Nanling, YGG, Lingnan and C. China at genus level, while the similarity coeffcientof species was in order Lingnan, YGG, C. China, E. China, and Nanling. The differencesin sequence of similarity coeffcients at family, genus and species levels might be caused by (1) the size of area was different in various comparative regions, and the equivalent area transformation was not calculated, (2) species investigation in various comparative re-gions was not accurate and identical; and (3) similarity coefficients in different taxa for explaining floristic relationship were not alike, which might be an important reason. Family and genus compositions in various comparative regions were obviously different, therefore, the similarity coefflcient at species level could better exhibit floristic relations among floras compared. In terms of geographical elements of genera, the floristic relations between C. China and E. China, Lingnan and YGG were close, while HGG was closely related to Nanling. Dendrogram of geographical elements of genera indicated that close relation occured between HGG and Nanling floras, and the relation of HGG to Lingnan and YGG floras was closer than that to C. China and E. China. The results obtained by geographical elements of genera differed obviously from those by similarity coefficients of family, genus, especially species, the reason of which was that the minimum spanning tree and dendrogram explained only the quantitative relation of geographical elements of genera between floras instead of similarity of other taxa between floras,