Abstract: The method of principal component and cluster analysis were combined to investigate the variation characteristics of Sichuan dark tea quality ingredients during post- fermentation.The results showed that the first two principal components accounted for 84.977% of the total variation. The first principal component was mainly affected by the levels of caffeine and water soluble pectin, the second principal component was mainly affected by the levels of theaflavin, theabrownin and amino acid.The period of post- fermentation was classified into 3 stages by hierarchical clustering: stage I was the beginning of post fermentation ( 0d) ; stage II was from the 3rd day to the7 th day; and stage III was from the 9th day to the end of post- fermentation. It was demonstrated that the transformation of the quality ingredients of Sichuan dark tea had been almost completed after the 1stturning and mixing ( Fandui) operation. Water soluble pectin, caffeine, theaflavin, theabrownin and amino acid were the key ingredients affecting the quality formation of Sichuan dark tea.