Abstract: In this study,the staining effect and adsorption performance of the juglone on hair were compared in the presence of gallic acid.The interaction energy between juglone and hair keratin was calculated by constructing molecular models,and the effect of gallic acid on it was studied.The aim is to explore the mordant mechanism of gallic acid on juglone.The experimental results showed that gallic acid could make the hair color brighter and have stronger color fastness.At the same time,gallic acid can also change the adsorption behavior of juglone,increase the total amount of adsorption.Gallic acid act as a bridge linking hair keratin and juglone,making the overall energy lower and forming many more stable hydrogen bonds.It was indicated that gallic acid can act as a mordant to enhance the dyeing performance of juglone.This study provided a theoretical basis for the selection of natural mordants.

Key words: gallic acid, juglone, fastness, adsorption, mordant