The lairage process can significantly affect the quality of meat. The yield of mutton is relatively large in China. So it is necessary to strengthen the exploration in this respect. The effects of different lairage times (0h, 3h, 6h, 12h, 18h and 24h) on stress level and mutton quality of Small Tail Han sheep after 5h transportation were compared. The suitable lairage time was established and it was meaningful in mutton production. The results showed that 12h lairage could increase the glycogen content to (7.74±0.98)mg/g, decrease the final pH value to 5.57±0.14, and improve the tenderness of mutton. The plasmacortisol and creatine kinase contents were slightly increased and then decreased with the extension of lairage time. The lowest data could be seen in the 12h lairage group, which were (39.98±5.04)ng/mL and (277.64±19.88)U/L, respectively, indicating that Small Tail Han sheep could be relieved from stress caused by transportation. In addition, with the extension of lairage time, the weight loss of Small Tail Han sheep was increased. The concentrations of hemoglobin and hematocrit were increased to (40.63±0.85)% and (14.01±0.23)g/dL, respectively after 24h lairage, indicating that new stress was caused because of the extension of lairage time. Therefore, combined with the above indicators, 12h lairage time could ensure the minimum weight loss of Small Tail Han sheep and make them relieve from stress, improving mutton quality. The research was of great significance to the formulation of standards for mutton slaughtering industry and the guidance of mutton production.