Most oral cancers caused by oral mucosal fibrosis are located in superficial locations of the oral cavity, which can be perceived, seen and felt by patients. If timely preventive treatment is available, not only the cure rate is very high (the cure rate of early stage patients can reach more than 95%), but also the treatment has few complications, minimal sequelae and low cost. The main changes are fibrous degeneration of connective tissue, which can be divided into 4 stages: ① the earliest stage: some fine collagen fibers appear, and there is obvious edema, blood vessels sometimes dilated and congested, with neutrophil infiltration; ② early stage: immediately below the epithelium there is a collagen fiber glassy degeneration band, and then below there is collagen fiber interstitial edema, with lymphocyte infiltration; ③ middle stage: moderate glassy degeneration of collagen fibers, mild edema, and There is lymphocyte and plasma cell infiltration; ④Late stage: all glassy degeneration of collagen fibers and vascular narrowing or occlusion. Epithelial atrophy, shortening or disappearance of epithelial pegs, some epithelial hyperplasia, hypertrophy of pegs, vacuoles in epithelial cells, and sometimes abnormal proliferation of epithelium. In patients with severely impaired open mouth, a large amount of muscle fiber necrosis was seen (Figures 14 and 15). Electron microscopy showed widening of the epithelial cell gap and a large number of free bridging grains or cellular debris were visible. The number of mitochondria was significantly reduced, and some of them were swollen, distorted or disappeared in the form of vacuoles. Collagen fibers were proliferated in large numbers and distributed in bundles, and some collagen fibers were arranged in a disorganized manner. In severe lesions, the collagen fibers are degenerated, and the periodic transverse lines disappear or even focally disintegrate.