Abstract: To investigate the effects of different proportions of mixed silage of Lolium perenne L. and Medicago sativa L. on fermentation quality and nutritional value, a completely random design was used. The mass ratio of Lolium perenne L.（A） to Medicago sativa L.（B） was set to 10∶0(group A₁₀B₀), 6∶4（group A₆B₄）, 5∶5（group A₅B₅）, 4∶6（group A₄B₆） and 0∶10(group A₀B₁₀) for silage with 3 repetitions in each group. The fermentation quality（pH values, contents of lactic acid, acetic acid, propionic acid, butyric acid, ammonia nitrogen/total nitrogen and V-score） and nutrient composition（contents of dry matter, crude protein, soluble carbohydrates, neutral detergent fiber acid detergent fiber, crude ash and crude fat） were measured after 40 days of silage. The results showed that the pH value, the contents of acetic acid, the contents of propionic acid, and ammonia nitrogen/total nitrogen were the lowest in the group A₁₀B₀; Butyric acid was not detected, while lactic acid content was the highest. The pH value, acetic acid content, propionic acid content, butyric acid content and ammonia nitrogen/total nitrogen were the highest in the A₀B₁₀ group, while lactic acid content was the lowest. The pH value, acetic acid content and ammonia nitrogen/total nitrogen in each group showed a significant upward trend with the increase of the ratio of Medicago sativa L.（P＜0.05）. Lactic acid content was significantly decreased with the increase of the ratio of Medicago sativa L.（P＜0.05）. The content of propionic acid was between 0.24% and 0.29% and the change was not obvious. In terms of V-Score, the V-Scores in the group A₁₀B₀ and group A₆B₄ were the higher, which were 92.31 and 85.66 respectively, indicating good grade. The V-Scores in the group A₅B₅ and group A₄B₆ were in the middle, and the grade was medium. The V-Scores in group A₀B₁₀ was the lowest, and the grade was bad. The contents of soluble carbohydrate neutral detergent fiber, acid detergent fiber, crude ash and curde fat in the group A₁₀B₀ were the highest, but the crude protein content was the lowest, which was significantly lower than that in the other four groups（P＜0.05）. The content of water soluble carbohydrates neutral detergent fiber, acid detergent fiber, crude ash and crude fat in group A₀B₁₀ was the lowest, while the content of crude protein was the highest, which was significantly lower than that in the other four groups（P＜0.05）. The content of crude protein in each group increased with the increase of the proportion of Medicago sativa L., while the content of water soluble carbohydrate, neutral detergent fiber, acid detergent fiber, crude ash and crude fat decreased with the increase of the proportion of Medicago sativa L. The content of water soluble carbohydrate of the group A₆B₄ was significantly higher than the group A₄B₆（P＜0.05） and slightly higher than the group A₅B₅（P＞0.05）.There were no significant differences in other nutritional components between the group A₆B₄,group A₄B₆ and A₅B₅（P＞0.05）. The results indicated that the mixed silage of Lolium perenne L. and Medicago sativa L. could effectively make up for the shortcomings of low content of crude protein in Lolium perenne L. single silage and poor fermentation quality in Medicago sativa L. single silage, so that the silage could retain more nutrients while ensuring the quality of silage. Combined with economic cost, this study commended that Lolium perenne L. and Medicago sativa L. be mixed silage at a mass ratio of 6∶4.