The causes of blood blisters in the mouth are: 1, eat too hot food or drink too hot water caused by scalding of the oral mucosa, capillary rupture, oozing blood accumulates under the mucosa to form blood blisters, 5-7 days after gradual absorption, blood blisters healing. 2, crabs, fish, shrimp and other foods containing hard shells or spines stabbed under the mucous membrane of the capillary, resulting in a large amount of blood exudation, the formation of a larger blood blisters, accompanied by bacterial infection develops into a hematoma, the need for local disinfection and systemic application of antibiotics. Local disinfection and systemic application of antibiotics are needed.3. Wearing newly made denture, due to poor covering and overlaying relationship, resulting in misalignment of occlusal relationship, it is easy to bite the lip and cheek mucosa, forming fresh blood blisters, and blood blisters gradually heal after adjusting the denture.