Coefficient of parentage among crop cultivars is one of major methods for evaluating genetic relationship and genetic diversity among crop cultivars. Coefficient of parentage was analyzed among the inbred indica rice cultivars which were released in different eras in South China. The result showed that the genetic diversity among the cultivars released in the past 50 years changed as a “W” shape. Three summits happened in pre-1957, 1970-1979, and 2000-2008, and two lowest happened in 1957-1969 and 1980-1989. The result of cultivars clustering analysis based on coefficient of parentage indicated the genetic relationships among the inbred indica rice cultivars and the characteristics of the cultivars evolution in South China. It was coincident with the characteristic of the cultivars improvement based on a few core parents in different eras. These indicated that the genetic diversity in the inbred indica rice cultivars changed as coefficient of parentage among inbred indica cultivars in South China and the genetic diversity had not increased or fall continuously in the past 50 years, but fluctuated in a limited range.