Mouth ulcers that never heal may be related to the type and characteristics of the ulcer. There are three common types of mouth ulcers: recurrent aphthous ulcers, traumatic ulcers and cancerous ulcers. 1. The characteristics of recurrent aphthous ulcers are recurrence and self-healing, the cause of which has not been clarified so far. According to the classification of the ulcers, the mild ones will heal in 10~14 days and the severe ones will heal in 1~2 months. Recurrent aphthous ulcers are mostly treated symptomatically and cannot be cured; 2. traumatic ulcers are caused by external trauma, such as intraoral stump root and crown, bad restorations, etc. They need to be healed after removing traumatic factors; 3. Cancerous ulcers represent tissues that have become cancerous and require surgical treatment and regular review. Some need to be treated with radiotherapy and chemotherapy after surgery. It is also possible that the ulcers recur and never get better. It is recommended to go to the stomatology department of a regular hospital for consultation and examination by a physician to make a clear diagnosis and treat the cause of the ulcer.