Abstract: As a kind of important free radical scavenger in plants, ascorbic acid (AsA) plays a very important role in reducing the damage to cells which caused by membrane lipid peroxidation, and enhancing the ability of plants to resist the adversity stresses. In this study, the biosynthetic pathway of AsA was analyzed and compared, and summary was made on the physiological function of AsA, including its effects on cell division and elongation, involved in cell wall formation as a coenzyme, its light protective effects, and as carrier in electron transfer and signal transduction. The protection mechanism and function of AsA in plants adversity stress (temperature stress, salt stress, biological stress, etc.) were systematically elaborated. Researches on AsA are important for researchers to acquaint with the effects of free radical scavenger on plant resistance function, and the mechanism of free radical scavenging. Besides, the limitation of AsA study on grass seed deterioration was put forward, and the development trend of AsA study was also analyzed prospected in this study.