Abstract: The study was conducted to screen the optimum formula of compound additive used for obtaining high quality alfalfa hay with high moisture by using orthogonal experimental design (L16(45) with 5 factors and 4 levels for each factor. The moisture of alfalfa hay at bundling was 72% to 73%. Five components (factors) of Na2SO4, K2SO3, K2SO4, a-amylase, and sodium bentonite were used in this study. The application levels for Na2SO4 were 6, 9, 13, and 18 g/25 kg hay; K2SO3 were 1, 4, 8, and 12 g/25 kg hay; K2SO4 were 0.2, 0.6, 1.2, and 1.6 g/25 kg hay; a-amylase were 0.01, 0.05, 1, and 1.5 g/25 kg hay; and sodium bentonite were 2, 4, 8 and 12 g/25 kg hay. In addition, in order to improve the palatability of alfalfa hay, 3g/25 kg forage of glucose was added into each compound additive treatment. All the components were applied according to the schedule of the orthogonal experimental design at baling stage of alfalfa hay, and the bales were stored for 60 d. After storage, forage samples were obtained from each treatment and used for the analysis of the effects of each component and their combination on the stored forage quality. The results showed that Na2SO4 and sodium bentonite were the two major factors influencing the quality of stored alfalfa hay; Na2SO4 could influence most chemical components of alfalfa hay, such as water soluble carbohydrate (WSC), neutral detergent fiber (NDF), acid detergent fiber (ADF) and non-protein N; K2SO4 played an important role in improving forage dry matter (DM), WSC, NDF and ADF; whereas, K2SO3 and a-amylase were not as good as K2SO4 in improving the quality of alfalfa hay. Sodium bentonite could improve the crude protein content in alfalfa hay and was the major factor that affected the contents of crude protein, non-protein N and ash in alfalfa hay. Based on the analysis of results from orthogonal experimental design, the optimum additive formula was comprised by 35.51% Na2SO4, 32.78% K2SO3, 1.64% K2SO4, 0.03% a-amylase, 21.85% sodium bentonite, and 8.19% glucose. Application of this compound additive at bundling of alfalfa hay with high moisture could maintain or increase the DM, CP, WSC and ash contents of the hay; and decrease the NDF, ADF and non-protein N in alfalfa hay after 60 d of storage. The application rate of this kind of compound additive was suggested to be 1.5 kg per ton of hay, and it will cost 10 to 15 RMB per ton of hay.