A large part of glaucoma patients who have been treated with topical anti-glaucoma drugs for a period have experienced dry eye of varying degrees. Preservatives in anti-glaucoma drugs, particularly benzalkonium chloride (BAK), are believed to play a major role in the development of dry eye in patients. Based on existing research, this paper summarizes several main mechanisms of benzalamine causing dry eye. BAK can directly acts on tear film and destroy tear film stability, resulting in tear evaporation increasing and tear film osmolarity elevating. BAK has cytotoxic effects on corneal epithelial cells, conjunctival goblet cells and meibomian gland cells, thus can affect the secretion of mucus and lipid in tear film. BAK can also cause chronic inflammation of the eye surface, leading to discomfort in patients. By exploring the mechanism of BAK causing dry eye, we hope to provide ideas for guiding the use of glaucoma and developing a new antiseptic system for eyedrops.(Int Rev Ophthalmol, 2021, 45: 420-425)