Abstract: In order to provide useful information for the cultivation of high fecundity breeds （strains） of Tan Sheep, a total of 549 blood samples recovered from the crossbred sheep （F2） of Tan Sheep and Hu Sheep were tested for the Fec^B gene by using PCR-SSCP assay. The results showed that the BB genotype was absent in the tested samples; the genotype frequency of B＋ and ＋＋ was 52% and 48%, respectively; the allele frequency of B and B＋ was 26% and 74%, respectively. Combined with the traditional breed selection method, the selection of male and female crossbred sheep both with B＋ genotype could significantly improve the genotype structure and gene frequency of Fec^B gene, and was favorable for increasing the litter size of the crossbred sheep population.