Oral cancer is the most easily detected, yet the most overlooked malignant tumor. In a narrow sense, oral cancer refers to squamous carcinoma that occurs in the tongue, floor of the mouth, palate, gums, cheeks and alveolar mucosa; in a broad sense, lip cancer and oropharyngeal cancer can also be included in oral cancer. Worldwide, the incidence of oral cavity and pharynx cancer is high, ranking 6th among all malignant tumors (after lung, stomach, breast, colon and rectum, and cervical cancer), with about 350,000 to 400,000 new cases each year. With a large population in China, the actual number of oral cancer cases is among the highest in the world, therefore, prevention and treatment of oral cancer is a difficult task before our eyes. The early symptoms of oral cancer are not obvious, and most of the patients do not have obvious conscious symptoms. Those who have the following conditions must be highly alert and should go to regular hospitals for examination in time. (1) Ulcers: If oral ulcers do not heal after 2-3 weeks or more, patients should go to hospital for examination. (2) Masses: Any unexplained masses in the oral cavity and in any part of the face and neck (including masses without pain or discomfort) should receive regular medical examination as soon as possible. (3) Change in color or shape of oral mucosa: white, red or black patches of oral mucosa, especially when these patches have rough surface, ulceration, hard nodules, raised edges or sudden increase in size, etc., are typical danger signs and must be taken seriously. (4) Restriction of mouth opening: If there is restriction of mouth opening, the cause should be carefully investigated. It may be caused by maxillary sinus cancer invading backward to the closed mouth muscle. In addition, cancer of tongue root, cancer of mandibular ascending branch and cancer of pterygopalatine fossa in deep oral cavity may show symptoms of mouth opening restriction or be accompanied by pain. (5) Loose teeth: Sudden loosening, loss of teeth, discomfort in the bite of food-chewing teeth; especially if there are asymptomatic loosening of several teeth at the same time, it often indicates a problem and should at least be examined by x-ray. (6) Alteration of tongue movement and sensation: Sudden onset of limited tongue movement, slurred speech, pain during speech and swallowing, or loss of sensation or numbness on the half side of the tongue, etc. should be identified as soon as possible. (7) If there is unexplained bleeding in the mouth several times, the cause of bleeding should be identified as soon as possible. It is worth noting that once the above situation occurs, patients should go to regular hospitals for examination and treatment in time, because oral cancer is highly invasive and metastatic (mainly through lymphatic route), and early diagnosis and first treatment of the tumor are crucial. Therefore, it is important to emphasize the correct diagnosis and regular standardized treatment for the first time, because if the first treatment is not chosen properly, it often affects the final prognosis of patients.