The invention discloses an adhering film against oral ulcer and a preparation method and application thereof. The adhering film comprises, by mass percentage, 0.1-99.8wt% of bioactive glass, 0.1-99.8wt% of adhesive and 0.1-60wt% of water repellent agent. The bioactive glass in the adhering film against oral ulcer has an antibacterial effect and can relieve pain and promote union of the ulcer surface. The adhesive enables the adhering film against oral ulcer to firmly adhere to the ulcer part, the stimulation to the ulcer surface caused by foreign matter is effectively isolated, and thus the pain is relieved. A hydrophobic layer makes the adhering film against oral ulcer not adhere to the surfaces of other mucous membranes such as the gingiva and only adhere to the ulcer surface, the residence time of the adhering film in the oral cavity is remarkably prolonged, the water absorption speed of an adhesive layer can be slowed down, the adhering film against oral ulcer maintains a long time membrane state at the ulcer part, the adhesion time is increased, and the adhering film further has an effect of promoting union.