The study attempts to explore the influencing factors and molecular mechanisms of feed utilization by studying the correlation between sheep feed utilization and several serum hormone concentrations and the expression of related genes in tissues. 15 individuals from the same group that F1 rams of small-tail Han sheep × Dorper sheep were selected, and the two groups were found to have extreme differences in feed utilization rate through feeding experiments. Serum indicators and related gene expression were measured, and differential analysis and correlation analysis were carried out. The results showed that there was a significant difference in feed utilization and average daily gain between the two groups（P＜0.01）. The neuropeptide Y（NPY） hormone concentration in high feed utilization rate group was significantly lower than that in the low feed utilization rate group（P＜0.05）. The NPY showed alow positive correlation（r=0.307, P＜0.05; r=0.447, P＜0.05） with feed consumption and feed utilization rate, and showed a moderate negative correlation with the average daily gain（r=-0.620, P＜0.05）. there was not significant correlation between hormone and feed utilization rate. The expression level of NPY gene in the high feed utilization group was higher than that in the low feed utilization group, which was consistent with the concentration determination in serum; NPY gene was most expressed in the rumen and the least in muscle. The results suggest that NPY may be one of the factors affecting feed utilization, and further research is needed for the intrinsic regulation mechanism.