Abstract: Black tea is a fermented tea.Amino acids and catechins are important components,which substances in fresh leaves changed,and formed a unique color,taste and aroma of Keemun Black tea in the processing.Samples from processing were studied.Catechins,theaflavins and aromatic were measured by High Performance Liquid Chromatography( HPLC) and Gas Chromatography- Mass Spectrometer( GC- MS),respectively.The results showed that catechins were reduced during processing,catechins content of drying leaves was 8.72% of fresh leaves. Firstly,theaflavins were increased,and then decreased during processing,which was increased by2369.91% in rolling leaves compared with fresh leaves and was reduced by 66.44% in drying leaves compared with rolling leaves.Sixty three kinds of aroma components were detected.Linalool,linalool oxide,benzyl alcohol,geranial,phenethyl alcohol,benzoic acid,geranic acid and methyl salicylate were primary aroma components of Keemun black tea,which accounted for 69.69% of total aroma.The results are benefit to understand metabolic rule of catechins and aromatic in processing,control processing,and improve quality of Keemun black tea.