The floristic similarities and differences of karst nature forests between Libo and Kaiyang, at Guizhou Province in subtropical zone, China, were studied based on field investigation and typical plots. The results showed that there are 827 species belonging to 408 genera and 146 families in Libo, and 838 species belonging to 434 genera and 150 families in Kaiyang, with 200 common species belonging to 227 genera and 118 families. The families and species percentage at family level were left-normal distributions, and the genera percentage at genus level was hyperbola distribution but species percentage was left-normal distribution. The differences in composition of families, genera and species in both areas indicated their heterogeneity of ecological condition and forest origination. The areal-type at genera level showed a left-normal change, and common genera for a hyperbola change, which the number of Tropical genera was more than that of Temperate. Due to the difference in latitude and altitude, the number of Tropical genera in Libo and that of Temperate genera in Kaiyang were higher. The ratio of species to families and species to genera in different areas were lower than those in Guizhou Province and China. Percentage of mono-specie families and mono-specie genera expressed oppositely trend. All these showed the ancient and solitary of karst nature forest floras.