This paper uses the data from the Sixth Population Census at national, provincial, prefecture and capital city levels to investigate China’s high SRB, the polarization of which is now spreading, and to discuss the latest changes of SRB in recent years. In regard to the abnormal SRB among first births, the paper analyzes the converging trend between urban and rural areas, among different regions, and from the perspective of women with different educational levels and different cohorts. It postulates that sex preference of fertility behavior at the first birth indicates that China's fertility transition has begun to enter a new historical stage and the pattern of fertility is largely motivated by social factors other than the policy ones. This paper further analyzes the distribution of gender composition for surviving children of women between 15-64 years old. The results show that the distribution is significantly and increasingly deviated from the normal one. Sex selection of fertility behavior increases the possibility of giving birth to a boy for couples over 1990 to 2010. China’s “son preference” becomes increasingly strong.