Objective To investigate the dynamic changes in the major non-volatile chemical components during the processing of Jianghua Kucha 21-3 Gongfu black tea.Methods Fresh one-bud-two-leaf autumn tea leaves of Jianghua Kucha 21-3 were used as raw materials. Samples at different processing stages were obtained by liquid nitrogen pre-freezing and freeze-drying. The mass fractions of water extract, tea polyphenols, catechins, theaflavins (TFs), thearubigins (TRs), theabrownins (TBs), caffeine, theanine, free amino acids, and soluble sugars were determined. Additionally, sensory evaluation was conducted on Gongfu black tea processed with different fermentation durations.Results During processing, the mass fraction of water extract in Jianghua Kucha 21-3 Gongfu black tea gradually decreased, reaching (39.19±0.30) g/100 g after drying. The mass fractions of tea polyphenols, catechins, and theanine also decreased progressively, with rapid declines occurring during rolling and the early stage of fermentation. In contrast, the mass fractions of TFs and TRs increased sharply during rolling and early fermentation, reaching maximum values at 2 h and 6 h of fermentation, respectively, at (1.35±0.02) g/100 g and (7.22±0.54) g/100 g. The mass fraction of free amino acids reached its maximum at 3 h of fermentation and then gradually decreased, while the mass fraction of caffeine remained relatively stable throughout the processing. Sensory evaluation revealed that fermentation duration had little effect on the appearance of Gongfu black tea but significantly influenced its internal quality. When fermented for 3~4 h, Jianghua Kucha 21-3 Gongfu black tea exhibited a mellow and brisk taste with a bright red liquor, indicating superior quality.Conclusion The optimal fermentation time for Jianghua Kucha 21-3 Gongfu black tea should be controlled at 3~4 h.