This study aimed to determine and estimate available energy value of peanut vine for mutton sheep using substitution and extrapolation methods, and find a proper substitution proportion of peanut vine in diet in substitution method, for the purpose of providing a reference for determination and estimation of available energy value of single straw feed. Fifty four healthy adult crossbreed wethers (Dorper×small-tailed Han F1) with body weight of (45.00±1.96) kg were used in a randomized block design. The wethers were divided into nine groups with six replicates per group and 1 sheep per replicate. Sheep in different groups were fed basal diet, full peanut vine diet and experimental diets using different proportions (10%, 20%, 30%, 40%, 50%, 60%, and 70% respectively) of peanut vine to substitute basal diet. The adaptation period lasted for 10 d; the experimental period lasted for 9 d, including 3 d of gas metabolism test and 6 d of digestion and metabolism test. The results showed as follows:1) no significant difference was found in dry matter (DM) apparent digestibility among 20%, 30%, 40% groups and full peanut vine diet group (P>0.05), while these groups were significantly higher than the other groups (P<0.05). Apparent digestibility of organic matter (OM) of full peanut vine diet group had no significant difference with that of 20% group (P>0.05), and was significantly higher than other groups (P<0.05). Apparent digestibility of gross energy (GE), neutral detergent fiber (NDF), acid detergent fiber (ADF) and ether extract (EE) of full peanut vine diet group were significant higher than those of 10% group (P<0.05), while apparent digestibility of crude protein (CP) was significantly lower than that of 10% group (P<0.05), and all of them had no significant differences with the other groups (P>0.05). 2) Digestive energy (DE) and metabolizable energy (ME) of peanut vine showed a similar trend, which was full peanut vine diet group (8.57 and 6.69 MJ/kg DM) had no significant difference with 20% (8.22 and 6.58 MJ/kg DM), 30% (8.02 and 6.50 MJ/kg DM), and 40% groups (8.10 and 6.52 MJ/kg DM), but these groups were significantly higher than the other groups. 3) The 'true' ME of peanut vine calculated by extrapolation method was 6.62 MJ/kg DM, which was close to ME form substitution method. It is concluded that the substitution method can be used for the calculation of DE and ME of peanut vine as a single forage for mutton sheep; the appropriate substitution proportion of peanut vine (straw feed) in diet is 20% to 40% for determination of available energy value.