Abstract: There still exists remarkable difference on yak’s taxonomic status in Bovinae. Primers designed according to the Mitochondrial gene sequences of Bos taurus reported was used to amplify and sequence yak’s Cytochrome b gene, and the whole sequence of Cytochrome b gene was obtained .Using Ovis aries as outgroup taxa, the Phylogeny about the representative species of Bovinae was analyzed .The results showed that among different species the transition/transversion(Ts/Tv) of Cytochrome b gene was 4.9, suggesting that the mutation was not saturation; the percentage nucleotide sequence divergence between yak and Bovinae was 8.0%~8.6%，which was more than that of yak and Bison bison; Phylogeny analysis found that Poephagus grunniens and Poephagus mutus clustered first of all, then gathered with Bison bison, indicating there was higher genetic comparability than that of Bos, the results sustained the idea Poephagus grunniens and Poephagus mutus owned one ancestor —primitive yak;The approximate divergence time between these two species was 0.55 million years. The data also supports the point that yak is classified as Poephagus of Bovinae, Poephagus including two species: Poephagus grunniens and Poephagus mutus.