Taking analogy is a way for the ancients to understand things. That is, through the commonality of related things in nature to deduce the nature of other unknown things. Although this method has a subjective tendency, it is often used very effectively in Chinese medicine and traditional Chinese medicine. For example, Zhang’s theory on leech: black in color, fishy in smell and rotten in taste, it is best at entering blood, but its fishy and rotten taste is inductive with stagnant blood, but not with new blood, so it is best at breaking stagnant blood without hurting new blood, and because it devours blood with its body (other things devour blood with their mouths), so its power of breaking blood is especially great; Huangqi, sweet in taste and warm in nature, has the nature of ascending, so it is best at nourishing liver qi (liver in the season should be spring, the main ascending), this is the same qi seeking each other; cicada is good at singing, and cicada molting is good at treating It is good at treating hoarseness caused by throat diseases, which is the same as the sound; because it is the shell shed by cicadas, its quality is very light, so its nature is good at going to the surface and treating superficial evidence. There are also vines that are good at soothing the meridians and activating the collaterals, and flowers that are good at regulating the emotions and clearing the head and eyes, all of which belong to the application of the method of taking analogies in traditional Chinese medicine.