Based on strain-cultivar reaction the pathogenicity of 75 Xanthomonas oryzae pv. oryzicola (Xooc) strains collected from different areas in southwest China was identified. The virulence against the differential varieties of IRBB4, IRBB5, IRBB14, IRBB18, IRBB21 and IR24 were inoculated into flag leaves of rice by using leaf needling for lesion length measurement. It showed that the virulence of these strains was differentiated distinctly; It also suggested that the 75 Xooc strains can be classified into 13 race groups: (1) RRRRRR, (2) RRRSRS, (3) RRSRSS, (4) RRSSSS, (5) RSRRSS, (6) RSRSSS,(7) RSSRSS,(8)RSSSRS, (9)RSSSSS,(10)SRSSSS, (11) SSRSSS, (12) SSSRSS, (13) SSSSSS, which was designated as C1-C13, respectively. Weak reaction patterns were proved mainly between pathogens and rice varieties and some strong interaction was discovered. The results further indicated that the predominant race C9 was distributed in all three provinces, and all 13 race groups were distributed in Yunnan, race 6,11,13 in Guizhou, race 3,4,6,7, 11,12,13 in Shichuan. The race distribution of Xooc in 3 different provinces is affected by geographic differentiation.