Abstract: The relationship between structure and stability of 16 different kinds of natural pigment was studied in this paper. The factors affecting its stability were systematically studied, such as light, oxygen, temperature, metal ions, medium polarity and pH value. It showed that instability behavior of aromatic compound and aliphatic compound, fading or changing mechanism, main affecting factors and so on were essentially different, and a good many complementary traits of the two types of natural pigment and variable disciplines between theoretical arithmetic heat of formation of some natural pigments and their light stability were also discovered. So the classification of natural pigment by dichotomy is first put forward, which is to forecast, increase and improve the stability of natural pigment and promote the process of replacement of unhealthy synthesis pigment by natural pigment.

Key words: natural pigment, dichotomy, relation between structure and behavior