This research is mainly probing the slave society institution of Yi Ethnic in Liangshan. This is a completely economic exploiting institution. In Liangshan areas, Yi Ethnic divided their social members in two classes-ruler and slave; then subsidiary divided in five levels. By this institution, there is completely exploited slave freedom by occupy institution on the whole. They even didn't have basically personally freedom in slave level. Everything was dominated by slave owner. However, slave owner for the sake of their personal and social plentiful, used a lot of unreasonable and cruel artifices to suppress slave. But even so such kind of unfair institution had existed in west southern parts of China for more than two thousands years. Till 1954's, the liberation army occupied Liangshan districts, slave had have real freedom.