Abstract: The auther made an analysis of genetic relationship of the ancestors with their derivative cultivars released in Guangxi, and calculated their coancestry coefficients in this paper. The results showed that the total 12 soybean cultivars and 5 breeding lines released in Guangxi during 1981~2005 can be traced back to 25 ancestors. Among them, 8 were landraces, 14 unknown strains from other provinces, and 3 exotic introductions, one cultivar can be traced back to 2.9 ancestors average. Many ancestors only derived a cultivar, but a few ancestors have derived more than two cultivars. For example, Jingxi Soybean derived 7 cultivars, Beijing Soybean 6, PingGuo Soybean 3 and so on. Single cross are key breeding models in Guangxi, there are 16 from this model among the total 17 strains.