IAA is used as plant growth stimulant and analytical reagent. 3- indolyl acetic acid and 3- indolyl acetaldehyde, 3- indolonitrile, ascorbic acid and other auxin exist naturally in nature, and the precursor of 3- indolyl acetic acid in plant is tryptophan. The basic function of auxin is to regulate plant growth, not only to promote growth, but also to inhibit growth and organ formation. Auxin exists in plant cells not only in free state but also with bound auxin, which is firmly combined with biopolymers, and also with a combination of specific substances, such as indolyl acetyl asparagine, indolyl acetate amyl glucose and indolyl acetyl glucose.