Corneal fistula is one of the complications of keratitis. It is not a fistula, but rather a loose tissue embedded in a corneal perforation from which atrial fluid exudes through the fissure. It is most likely to occur in patients whose pupillary rim is embedded in the area of corneal perforation. The main signs are a dark black bulge on the corneal surface, loss of the anterior chamber, and softening of the eye. Keratitis is divided into two categories: ulcerative keratitis, also known as corneal ulcer, and non-ulcerative keratitis, or deep keratitis. Keratitis is caused by different factors such as internal and external causes. It is an inflammatory disease caused by corneal trauma, bacterial and viral invasion of the cornea. This article focuses on the diagnosis of corneal fistula. Corneal fistula examination and diagnosis methods: fluorescein staining method corneal, conjunctival epithelial damage or ulceration, can be fluorescein staining, the method is to point sterile 1% fluorescein solution in the conjunctival sac, and then rinse with saline, can also use a glass rod dipped in a small amount of liquid in the conjunctival sac, for observation. At this time, the cornea and conjunctiva can be seen to have a soft green coloring at the rupture, and no staining at the epithelium intact. If there is a corneal fistula, point fluorescein after making light pressure on the eye, the corneal surface can be seen covered with yellow-green fluorescein, while at the fistula there is fluid flow, like a clear spring outflow. During the operation, care should be taken not to contaminate the face and clothes of the subject. Since fluorescein is easily contaminated by bacteria, recently it is advocated to use sterilized fluorescein filter paper, which is soaked with saline at one end and then in contact with the conjunctiva, the tear fluid is yellowish green and the corneal injury is stained.