The experiment was carried out to study the effects of adding lactic acid bacteria (LAB) (fast-sile, FS), previous fermented juice (PFJ), sucrose (S) and FS+S on the fermentation quality and the amount of LAB during ensiling of alfalfa silage. There were 5 groups including control, FS (0.000 5%), PFJ (0.2%), S (1%) and FS+S (0.000 5%+1%), respectively. The fermentation qualities were analyzed on day 2, 5, 10, 15, 30 and 45 after ensiling, respectively. The effects of additives on fermentation quality of alfalfa silage were observed. The sequence for the effects of additives was: FS+S>S>PFJ>FS. The amount of LAB in all additive groups was higher than that in control group after the storage of 45 days (P<0.05). There was higher amount of LAB in FS group compared with the other groups. The pH in control group decreased during the first 5 days, and then increased gradually until the end of ensiling. The pH in additive groups decreased quickly, and then kept at the low level during ensiling. The changes of organic acid composition were consistent with the change of trends of pH. NH3-N/total N in all groups increased gradually, which increased slowly after 10 days, whereas that in the control group showed greatly increase. In conclusion, additives contributed to improving quality of ensiling, and advancing effect of supplementation of LAB and sucrose simultaneously was best in all groups.