Abstract: This study applied solid-state fermentation with Monascus to black highland barley bran to enhance its utilization. The fermentation process was optimized by monitoring the antioxidant potency composite (APC) index. Comparative analysis of unfermented samples and those from the optimal fermentation time point was conducted using headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) to systematically profile volatile flavor compounds and untargeted metabolomes. The results demonstrated that the contents of total polyphenols and total flavonoids exhibited an initial increase followed by a decrease during fermentation. In contrast, compounds including 4-hydroxybenzoic acid, p-coumaric acid, luteolin, and its glycoside derivatives peaked in the unfermented samples and declined continuously thereafter. Levels of cis- and trans-ferulic acid, as well as protocatechuic acid, also showed an initial increase followed by a decrease. Based on the APC assessment, the optimum fermentation duration for black barley bran using Monascus was established at 5 days, achieving an APC of 98.45%. A total of 215 volatile compounds were identified. Fermentation led to significant increases in the relative contents of esters, ketones, alcohols, aldehydes, and phenols. A total of 2914 differential metabolites were identified in the untargeted metabolomics analysis (VIP≥1, FC≥2 or FC≤0.5, and P<0.05). Compared to the unfermented group, 1671 metabolites were significantly upregulated (P<0.05) in the 5-day fermentation group, with the most notable change observed in the content of 8-deoxyanthocyanin. KEGG pathway enrichment and correlation analyses indicated that fermentation effectively enhanced the flavor profile of black highland barley bran, providing a theoretical foundation for its development into functional foods.