Abstract: In order to study the effect of dietary on the bacteria in the rumen of cows, nine different concentrate diets were used to feed Holstein cows during the dry period. Partial aerobe and facultative anaerobe were isolated, identified and detected. Five health cows were fed continuously in nine periods. The results showed that 56 strains of bacteria were isolated from the rumen fluid by artificial medium, and the 16S rDNA genes of 7 strains of representative bacteria were amplified by PCR. These bacteria were S.bovis(A0625, A1212, 0131), B.cereus(0113), B.licheniformis(0091), B.pumilus(0083) and S.thermophilus(0123) respectively by sequence homogeneous analysis. At the same time, the quantities of S.bovis, Bacillus and S.thermophilus were increased as the increase of concentrate. The results demonstrated that the dietary of different concentrate has different effects on the quantity of aerobe and facultative anaerobe in the rumen, and the quantities of S.bovis was affected significantly. New evolutive branch of bacteria was not shaped by the phylogenetic analysis, however, there were several mutations in the nucleotide sequences of the S.bovis and S.thermophilus.