Based on the data of the 4th and 5th national census, this paper reviews the changing process of fertility level and birth sex ratio of Chinese Minorities from 1980 to 2000 by indirect estimation, explores the trend of birth sex ratio during the fertility level declines1 Taking Moguls, Hui and Unger as examples to explore the relationship, the resultindicated the sex ratio at birth is highly correlated to fertility when the fertility level is getting into lower level.