Abstract: In order to study the optimum conditions for yellow silage fermentation of maize straw in Baotou region of Inner Mongolia, and to evaluate the feeding effect of the formula diet with supplementation of the prepared yellow silage on fattening sheep. Laboratory experiments on microbial fermentation agent, fermentation time duration and fermentation excipients were carried out using a three-factor and three-level orthogonal test to screen the best fermentation combination; according to GB/T 20807-2006 Concentrate for Sheep standard, the formula diet containing different proportions of yellow silage was prepared, and a feeding experiment was carried out to compare the fattening effect of traditional fattening sheep feed and formula diet supplemented with yellow silage of maize straw on Small-tailed Han sheep. The results showed that the order of the three factors influencing the pH value of yellow silage was as follows： fermentation excipient〉fermentation microbial agent〉fermentation time duration; the best combination of fermentation conditions was liquid EM fermentation microbial agent ＋fermentation 25 d＋salt; the live weight, carcass weight and single ocular muscle area of the sheep fed with different proportions of yellow slige in basal diet were significantly higher than those fed with traditional fattening diet （P〈0.05）; the feed conversion rate of sheep fed basal diet with 40% yellow silage was significantly higher than that of control group （P〈0.05）; the slaughter rate of sheep fed with 20% yellow silage in basal diet was significantly higher than that of control group （P〈0.05）; there were no significant differences in daily weight gain, thigh muscle thickness, waist muscle thickness and water holding capacity between the two experiment groups （P〉0.05）. Considering the feeding effect and the feeding cost, the best fattening effect for Small-tailed Han sheep was to add 40% into the basal diet.