In order to investigate the effect of snow cover on alfalfa overwintering and turning green, 6 different alfalfa varieties (including Longmu 806, Gongnong No. 1, Aohan, Wega 7F , WL319 HQ, Caoyuan No. 3) were used as plant materials. There were 4 treatments in this study include snow-cover of 0, 30% , 70% and natural snow-cover ( used as control). Nutrient content and antioxidant enzyme activity of root were measured before and after overwintering period. The rate of plant returning green and growth rate after greening were also measured after turning green. The result showed that the snow cover was the guarantee of alfalfa safely overwintering and turning green. The 54.5 -77.9 cm snowfall was the optimum thickness of snow for safe overwintering. Alfalfa improved the overwintering ability by enhancing the root nutrients and antioxidant enzyme activity, and it was affected by snow cover. In addition total nitrogen and soluble sugar increased by 61% and 60% respectively, soluble protein reduced by 8 % , SOD and CAT reduced by 20% and 9% respectively than that before the overwintering under 70% of natural snow-cover. There were differences between overwintering ability of 6 different alfalfa varieties, in which Caoyuan No. 3 has more grass production and Wega 7F has stronger overwintering ability.