Abstract: In this study, crushed black teas with different fermentation degrees were examined. Sensory evaluation, quantitative flavor assessment, and chemical detection were integrated to systematically explore the optimal fermentation duration for the quality of crushed black tea. The overall quality of crushed black tea initially increased and then decreased as fermentation time increased, with the 120-min-fermented sample exhibiting the best quality. Regarding major internal components, tea polyphenol content decreased as fermentation progressed, from 258.59 mg/g in withered tea samples to 157.43 mg/g after 4 h of fermentation. Soluble sugar content increased markedly during early fermentation stages, reaching 28.36 mg/g in the withered samples, and then remained stable at approximately 34 mg/g during subsequent fermentation. Free amino acid content showed no obvious fluctuations among samples with different fermentation degrees. After 120 min of fermentation, tea polyphenols remained relatively low, whereas soluble sugar and free amino acid contents increased significantly in FJ90 min, contributing to better overall quality of tea infusions. Using liquid chromatography coupled with high-resolution mass spectrometry, 214 compounds were identified in the crushed black tea. Using the dual criteria of VIP>1 and P<0.05, 75 key differential compounds were screened. Correlation analysis indicated that tryptophan, aroma glycosides, catechins, theaflavins, trans-3-indoleacrylic acid, 4-vinylpyridine, pyruvic acid, and most flavonoids and flavonoid glycosides were strongly positively correlated with the sour flavor of crushed black tea. Triethyl phosphate, together with flavonoid components—including chalcones, naringenin, and isorhamnetin—was highly correlated with the bitterness and flavor intensity of crushed black tea. This study confirmed that crushed black tea fermented for 120 min possessed the best comprehensive quality; insufficient or excessive fermentation time adversely affected the flavor of crushed black tea. In actual production using standardized mechanical equipment, 120 min can be used as the standard fermentation time for high-quality crushed black tea.