Aiming at low utilization efficiency of corn and broom sorghum straw raw materials in rural Balin Left Banner， Chifeng， and beef cattle malnutrition caused by farmers' lack of dietary knowledge， this study explored changes in nutritional quality，fermentation characteristics，in vitro digestibility and microbial community of total mixed rations（TMR）with different straw ratios during room-temperature storage，to provide basis for straw feed utilization and beef cattle feeding. Five groups with corn straw：broom sorghum straw raw ratios of 9∶1，8∶2，7∶3，6∶4，5∶5 were set，mixed with concentrate to prepare TMR with 50%moisture content，sealed in ethylene plastic bags.Samples were collected at 0，2，5，7，10，15 days（3 replicates per group）for index determination and sequencing. with prolonged storage， dry matter（DM），crude protein（CP），water-soluble carbohydrates（WSC），neutral detergent fiber（NDF），and acid detergent fiber（ADF）of all groups decreased（P<0.05），and DM loss was lower in high broom sorghum straw raw groups； pH increased with trace detected propanoic acid and butyric acid （P<0.05）；after 2 days， bacteria were dominated by Pantoea（increasing pH）and Bacillus（promoting DM loss），while fungi were dominated by Alternaria and Clavispora（causing mildew，positively correlated with nutrient loss）. TMR decays within 2 days at room temperature；low broom sorghum straw raw groups are prone to deterioration due to WSC depletion，while high-ratio groups delay decay but have insufficient acidification. Proliferation of aerobic bacteria and molds is the key for the decay. It is suggested to select high broom sorghum straw raw formula for short-term feeding， and to use airtight packaging and control storage time.

Straw  /  Total mixed ration  /  Fermentation  /  Nutritional quality  /  Fermentation quality  /  In vitro digestibility  /  Microbial community dynamics