Abstract: Twenty-four first filial generations (F1) sire growing-fattening sheep cross-breeds (Chinese Inner Mongolian Fine-wool and German Mutton Merino) averaging 3.0 months old and 23.1±0.62 kg body weight (BW) were arranged into four random groups. Sheep in the control group were fed concentrate supplement and silage maize, whereas sheep in treatments Ⅰ, Ⅱ and Ⅲ were fed concentrate supplement and silage maize, of which 1/3, 2/3 and 3/3 were substituted with grass-mixtures of Elymus dahuricus Turcz, Puccinellia distans (L.) Parl and Astragalus adsurgens Pall cultivated in hyper-alkali-saline grasslands. The feed intake, average daily gain, feed digestibility and slaughter performance of sheep in different groups were investigated. The results show no significant effect of mixed-grass feed on average daily gain (P>0.05). Feed intake in treatment Ⅲ is higher than that in the control (P<0.05). Feed conversion rate in treatmentsⅡand Ⅲ is higher than that in the control (P<0.05). Digestion of dry weight, organic matter, ether extract, neutral detergent fiber and acid detergent fiber linearly decreases with increasing mixed-grass feed proportion (P<0.05). Digestible nitrogen, retained nitrogen and retained-to-digestible nitrogen ratio also linearly decrease with increasing mixed-grass feed proportion (P<0.05). Percents of dressing and meat in treatments Ⅰ and Ⅱ are higher than those in treatment Ⅲ and the control (P<0.05). Meat-to-bone ratio in treatmentsⅠand Ⅱ are higher than those in the control (P<0.05). Eye muscle area in the treatments is significantly higher than that in the control. The above results indicate that though different levels of mixed-grass feed have no effect on average daily gain, they decreases feed digestibility and nitrogen utilization in sheep. Percents of dressing and meat, meat-to-bone ratio and eye muscle area improve when sheep are fed with mixtures of silage corn and mixed-grass feed.