Abstract: The effects of formic acid and previous fermented juice on fermentation and nutrient of baled alfalfa silage were studied. The wilted forage as CK, the amount of formic acid and previous fermented juice were 6 L/t and 2 L/t, respectively. Unchopped alfalfa baled and wrapped with 6 layers stretch film. After storage 300 d, the bale opened and sampled to analyze fermentation quality and nutrient value. Compared with formic acid and previous fermented juice treatment, which the pH value were 4.32 and 4.25, the wilted alfalfa silage pH increased significantly to 5.22 （P<0.05）. The lactic acid contents were 6.26% and 6.63% for formic acid and previous fermented juice treatments, which were higher than that of wilted alfalfa silage of 0.24%（P<0.05）. But the wilted alfalfa silage had the lowest ammonia nitrogen（P<0.05）. No difference of NDF, ADF in all treatment, adding formic acid improved significantly effective degradability of DM, OM, CP, NDF, ADF (P<0.05), wilted treatment decreased significantly effective degradability of DM, OM, CP, ADF (P<0.05) and with lower CP content.