Abstract: Abstract: Switchgrass (Panicum virgatum L.) is a warm-season perennial bunchgrass, and the crude protein content of its whole pant is higher than the whole plant of soybean. It is a kind of excellent grass as a livestock feed, which not only has high yield and outstanding quality, but also shows very strong tolerance or resistance to the adverse environment. Lactic acid bacteria (LAB) are often added to forage crops for improving the silage fermentation at the ensiling period, and LAB community has been widely used to prepare the fermented feed, such as alfalfa, crop stalks, bagasse and manioc waste. However, few studies have been done about the effect of LAB on the characteristics of switchgrass silage. Considering the selectivity of inoculants, a stable LAB community named SGL was detected from switchgrass silage by continuous restricted subcultivation. The results of the pyrosequencing showed that the major components in the SGL were Lactobacillus nantensis (78.78%), Lactobacillus plantarum (7.92%), Lactobacillus panthers (5.27%), Bacillus coagulans (4.41%) and Lactococcus lactic (3.31%), of which Lactobacillus plantarum (LP) is one of the most frequently used LAB species. The present experiment was conducted to investigate the effects of the SGL community or a single component Lactobacillus plantarum on the fermentation, microbial diversity and rumen fermentation of the resulting silage. Switchgrass was harvested by hand in mid-June when it was just in the vegetative growth stage (26.43% dry matter), and chopped to about 1.5 cm with a laboratory type chopper. The chopped forages were ensiled in 2 L anaerobic jars in the following treatments: control that is untreated, SGL and LP. SGL and LP were both applied in the same quantity of distilled water (10 mL solution per kg forage) at the dose of 1 OD600/kg of fresh forage. The control also received 10 mL water per kg forage forage. Three jars per treatment were sampled on the 3rd, 10th, 20th and 30th day after ensiling, for chemical and microbiological analysis. At the end of the ensiling period, i.e. the 30th day, the silages were subjected to an artificial rumen fermentation and an aerobic stability test at 25℃. The results indicated that the inoculation with SGL and LP both improved the fermentation, promoted the decline of pH value, decreased the concentration of NH3-N and butyrate acid, increased the concentration of lactic acid and crude protein in the silage, but decreased the concentration of acetic acid and reduced the aerobic stability. The 16S rRNA gene-based pyrosequencing was used to analyze the community of the resulting silage, and the results indicated that the diversity of microorganisms among different treatments had significant difference (P<0.05). Lactobacillus was the advantageous species, and Enterobacter were inhibited effectively in both SGL and LP. Rumen fermentation characteristics were determined by 48 h artificial rumen technique, and the results showed that the inoculation with LAB improved the in vitro dry matter digestibility, pH value, NH3-N and volatile fatty acid (VFA) concentrations were all within normal limits, and the total VFA concentration was SGL>LP>CK, so was the acetic acid and propionic acid. However, the addition of community SGL decreased the pH value more rapidly and had better effects on both silage quality and rumen fermentation, when compared with the single component LP. For SGL consists of variety of components, the interaction mechanism of components during the silage fermentation and the effect of switchgrass silages treated with SGL on the performance of the livestock need more study.