Abstract: Utilization of local grass in cold area and adherent lactobacillus germplasm resources to make Previously Fermented Juice (PFJ) has important significance to modulate high quality silage and solve seasonal feed-animal imbalance in the Tibetan region. In this study, we collected Kobresia littledalei from different altitudes (four areas) in the Tibetan region: (1) 5100m, Namtso; (2), 4682m, Gulu; (3), 4280m Dangxiong; (4), 3 980 m, Deqing. Kobresia littledalei was used as raw material to make PFJ; the PFJ was then added to production and equivalent distilled water as a control group to make alfalfa silages. Each processing repeated four times. The storage period was sixty days, and the fermentation quality and nutrition were determined after storage. Measurement indicators included count of lactic acid bacteria living cells in Kobresia littledalei at different altitudes, PFJ fermentation quality indicator (pH, Lactic acid, Soluble carbohydrate, Ammonium nitrogen, etc), fermentation quality and nutrition quality indicator of alfalfa silage added PFJ (pH, lactic acid, acetic acid, butyric acid, dry matter, crude protein, soluble carbohydrate, etc.) and level of protein decomposition of alfalfa silage added PFJ . Objective was to discuss the effect of previously fermented juice with different altitudes on fermentation quality and nutritional value of alfalfa silages. The results showed that count of lactic acid bacteria living cells in Kobresia littledalei and PFJ growing at different altitudes significantly increased as altitude increased (P < 0.05); the maximum count of lactic acid bacteria living cells in Kobresia littledalei was 1.57×109(Ⅰ) , and the maximum count of lactic acid bacteria living cells in PFJ was 12.60×109(Ⅰ). The influence of altitude on pH, lactic acid, soluble carbohydrate, and ammonia nitrogen of PFJ was significant (P < 0.05). The pH of higher altitude PFJ was lower. The pH of groupⅠwas minimum (3.63). Compared with the control group, adding PFJ can significantly reduce the pH value, acetic acid, and butyric acid contents of alfalfa silage (P< 0.05). The minimum pH value was 4.80 (Ⅰ) and the control group pH was 5.92. The alfalfa silage of lactic acid content increased with the PFJ; altitude significantly increased (P < 0.05), 508% in area (1), 394% in area (2), 409% in area (3), and 191% in area (4) and compared with control group, respectively. The maximum value of lactic acid was 9.73% (Ⅰ); the minimum control group was 1.60%. Compared with the control, soluble carbohydrate and dry matter contents of the alfalfa silage added four PFJ were significantly increased (P< 0.05), and they increased as altitude increased. PFJ in higher altitude Kobresia littledalei had stronger inhibition on protein decomposition in the process of silage of alfalfa; as a result, non-protein nitrogen (NPN) content of silage was lower (P < 0.05). Compared with the control, the true protein content of added group was significantly increased, and the non-protein nitrogen content and ammonia nitrogen content were significantly decreased. The most obvious decrease was peptide content (P < 0.05), while the free amino acids had a small increase(P < 0.05). The lowest NPN content was 54.28% in groupⅠ.In conclusion, adding Kobresia littledalei PFJ can improve alfalfa silage fermentation quality, inhibit protein degradation; the higher the altitude, the better the quality. It had an important role not only in improving the utilization of alfalfa silage protein, but also in providing reference for using local native grass resources for forage grass silage in cold area in future.