Objective To study the polymorphism and mechanism of GDF-9 and BMP-15 in mice of different strains, different reproductive capacity, and find out the relationship between genes and fecundity. Methods Screening polymorphism loci by using direct sequencing method, and testing 5 'UTR impact on downstream genes by constructing luciferase dual reporter vector. Results ICR mice litter size is about 2.8 times the BALB/c; In ICR and BALB/c, respectively, found three polymorphisms, one at the 5 'end of the non-coding region, the other two located in the protein coding region ; Dual-luciferase test results show that the 5'UTR area of GDF-9 can promote the expression of the downstream gene. Conclusions GDF-9 polymorphic loci exist in ICR and BALB/c strains, changes in these sites play a certain role in promoting the expression of the downstream gene.