Abstract: Alfalfa was used as the material to inoculate the selected lactic bacteria(LAB) community Al2, which is screened by continuous restricted cultivation in MRS media. Through extracting the DNA of bacteria in alfalfa silage directly, and amplifying the V3 region of 16S rDNA, the succession of inoculant on alfalfa was identified by using PCR-DGGE. And the dynamic changes of numbers of LAB, aerobic bacteria and mold were performed by plate isolation. From the results of DGGE, the predominant bacteria in natural fermented silage were Pediococcus pentosaceus, while the components of Al2 community, especially Lactabacillus plantarum were the predominant bacteria in Al2 treated alfalfa. Inoculating Al2 in alfalfa resulted in significant decrease in pH and ammonia-nitrogen content and improvement in LA production, and the fermented quality were improved.