Abstract: The objective of this study was to evaluate the effects of substituting hulless barley straw for tall fescue at different ratios on the early fermentation quality and aerobic stability of total mixed ration silage in Tibet. The experiment consisted of the control (TH₀) and three treatments (TH₅, TH₁₀, and TH₁₅). The silos containing these treatments were opened at 14 days after the start of ensiling and the fermentation quality, chemical composition, and microbial communities were analyzed. The aerobic stability of silage samples on the 2nd, 5th, and 8th day of exposure to air was evaluated using an online multi-channel data logger temperature recorder. The results showed that the pH, and the contents of lactic acid, acetic acid, total volatile fatty acids (TVFA), and alcohol did not differ significantly between TH₅ and TH₀ (P>0.05). The pH of TH₁₀ was similar to that of TH₀ (P>0.05), but the lactic acid, acetic acid, TVFA, and alcohol contents differed significantly between TH₁₀ and TH₀ (P<0.05). The lactic acid, acetic acid, propionic acid, butyric acid, TVFA, and alcohol contents were significantly lower in TH₁₅ than in TH₀ (P<0.05), while the pH of TH₁₅ was markedly higher (P<0.05) than that of TH₀. The ammonia nitrogen/total nitrogen and lactic acid/acetic acid ratios did not differ significantly (P>0.05) between all treatments and the control. Lactic acid fermentation was dominant in all silages and they all had good fermentation quality. During exposure to air, pH and the ammonia nitrogen/total nitrogen increased in all treatments and the control continued to increase after the 2nd day of exposure to air. However, the contents of lactic acid, acetic acid, and water soluble carbohydrates decreased during exposure to air, and the numbers of yeasts and aerobic bacteria increased. The temperatures in TH₅ and TH₁₀ silages began to increase at 35 h after opening the silos, while the temperature increase was delayed, and was smaller, in TH₁₅. Together, these results showed that TH₁₅ had the best aerobic stability. Taking into account the fermentation quality, aerobic stability, and maximum use of hulless barley straw, the TH₁₅ treatment was the most suitable choice for silage production.