Abstract: 【Objective】 This paper is to study the effects of diets with different cotton stalk levels on rumen fermentation parameters and slaughter performance of sheep during fattening period. 【Method】60 small tail Han sheep 6 month old weighing(43.08±5.93) kg were selected and randomly divided into 6 groups with 10 sheep in each groups. The experimental diet was formulated according to the principle of the same energy and the same nitrogen, CK1 group was not added with cotton stalk and cottonseed meal, CK2 group was added cottonseed meal, 20%, 30%, 40% and 50% groups were added with 20%-50% cotton stalk, respectively. The experimental period was 70 days. 【Result】(1) Rumen pH value of CK1 group was 6.25% higher than CK2 group, the difference was very significant (P<0.01),30% and 40% cotton stalk addition groups were higher 5.48% and 4.85% than CK2 group respectively, the difference was significant (P<0.05). (2) Rumen NH3-N concentration of 40% cotton stalk addition group was 40.44% (P< 0.01) and 39.40% (P<0.05) lower than CK1 and CK2 groups respectively, and 30% group was 26.89% lower than CK1 group, the difference was significant (P<0.05). (3) The concentrations of acetic acid, propionic acid, butyric acid and total volatile fatty acids in rumen were not significantly different among the treatments (P>0.05). The acetic acid and propionic acid ratio of CK2 group was34.58%, 31.69% and 35.69% lower than those of 20%, 30% and 40% cotton stalk addition groups respectively (P<0.01). The concentration of isobutyric acid of CK1 group were 195.31%, 243.64% and 220.34% higher than those of 20%, 40% and 50% cotton stalk addition groups respectively (P< 0.01). CK1 group was 166.19% and 182.09% higher than that of CK2 and 30% group respectively (P<0.05). The isovaleric acid concentration of CK1 group was 116.45%, 101.18%, 151.47% and 119.23% higher than those of CK2, 20%, 40%and 50% cotton stalk addition groups respectively (P< 0.01). CK1 group was 71.00% higher than that of 30% group (P<0.05). The valeric acid concentration was 178.05% higher than 40% cotton stalk addition group (P<0.05). (4) Dietary cotton stalk supplementation had no significant effect on live weight, carcass weight, slaughter rate, heart and testicular weight of sheep (P>0.05). The liver weight 20% group was 28.37% higher than 40% cotton stalk addition group (P<0.05). The spleen weight 20% group was 50.00% higher than CK2 group, 30%, 40% and 50% cotton stalk addition groups respectively, the difference was significant (P<0.05). The lung weight of 40% cotton stalk group was significantly lower than that of other treatments (P<0.05). The kidney weight of CK2 group was 42.85% lower than that of 20% cotton stalk group (P<0.01).The CK2 group was 22.22% lower than that of 40% and 50% cotton stalk groups, the difference was significant (P<0.05). 【Conclusion】The results showed that 20% cotton straw was suitable for sheep diet during fattening period.