Acetylcysteine is a mucolytic agent whose main function is to dissolve sticky sputum, which can reduce the stickiness of sputum and make it easier to expel. Acetylcysteine is clinically available in tablets, granules, capsules, injections, inhalers, etc. It is good for expectoration of large amounts of pus sputum caused by chronic obstructive pulmonary disease, emphysema, chronic bronchitis and other diseases. In addition, acetylcysteine can also be used to treat the early stage of liver failure, which can reduce bilirubin and improve prothrombin activity to achieve the role of liver protection, and also has a therapeutic effect on ophthalmic diseases such as punctate keratitis and herpes simplex keratitis.