Abstract: A study has been undertaken to investigate the microbial community structure, microorganism populations and diversity of lactic acid bacteria in Hordeum brevisubulatum silage. Lactic acid bacteria, coliform bacteria, aerobic bacteria, yeast and mold were isolated and counted by means of selective media. Lactic acid bacteria strains were identified by morphological observation, physiological and biochemical characteristics and partial 16S rDNA gene sequences. In order to assist the development of beneficial microorganisms for animal feed, the lactic acid bacteria strains with high fermentation performance were screened based on growth curves and their ability to produce and resist acid. The results showed that microorganism populations change in different ways through the fermentation process. Lactic acid bacteria populations increased from 0 to 4.00×10⁸ cfu/g FM and yeast populations grew from 8.50×10⁵ to 1.02×10⁸ cfu/g FM, whereas coliform bacteria, aerobic bacteria and mold populations did not change significantly. Four lactic acid bacteria strains were isolated from H. brevisubulatum silage which were identified at Lx36 isolation as Lactobacillus pentosus, at Lx37 isolation as L. brevis, at Lx53 isolation as Pediococcus pentosaceus and at Lx54 isolation as L. parabuchneri. Lx36 was screened out for high fermentation performance because it ceased to grow after 20 hours of cultivation, with an OD value of 4.21. The pH value of MRS broth (the bacterial growth medium) was only 4.08 after 12 hours of Lx36 cultivation, and the strain can survive in MRS broth with a pH of 3.0. These results indicate that silage fermentation is a process of microorganism interaction and that silage quality is directly influenced by the changing character of microorganism populations. Lactic acid bacteria species in H. brevisubulatum silage were relatively abundant. L. pentosus screened with a high ability to reproduce and to produce and resist acid, suggesting its potential value for practical applications.