The genetic diversity of 20 representative foxtail millet varieties, which were released in summer sowing region of North China since 1980s, were analyzed using 49 pairs of SSR markers. These SSR markers unlocked 142 alleles with a mean of 2.96 alleles per locus. The polymorphism information content (PIC) ranged from 0.0904 to 0.6896, with an average of 0.4168. The mean genetic distance was 0.4045 with a range from 0.0173 to 0.9000. These foxtail millet varieties were classified into 3 groups based on SSR assay. The variety Gufeng No.1 formed an independent group, suggesting a higher genetic distance of this variety to others. By investigating the genetic distances of foxtail millet cultivars that were released in different decades, the higher genetic diversity was observed in older varieties (1980s>1990s>2000s>2010s), which indicated a constitutive drop of the genetic variation in foxtail millet cultivars in breeding over last few decades.