Mouth ulcers with pustules under the tongue root can be treated with topical cotrimoxazole solution, oral vitamin C and other medications under the guidance of a doctor. Mouth ulcers with pus under the tongue root may be due to bacterial infection, oral mucosal injury and so on. 1. Compound Chlorhexidine Liquid: Compound Chlorhexidine Liquid has antibacterial and disinfectant effects. It is mainly used to treat gingivitis, pericoronitis, oral mucositis, oral mucosal ulcers and other symptoms. Long-term improper use may lead to the development of tooth coloring, yellow tongue, and altered sense of taste. Patients should follow the doctor’s instructions for medication. 2. Vitamin C: Vitamin C is mainly used for tissue repair, collagen formation and enhancement of immunity. It is usually used in the treatment of various infectious diseases and adjuvant therapy. Long-term improper use of vitamin C may cause adverse reactions such as red and bright skin, headache and frequent urination. Allergies are prohibited. Patients are advised to keep their mouth and teeth clean, maintain a regular routine and avoid staying up late. Eat more vegetables and fruits rich in vitamins and prohibit spicy and stimulating food. At the same time, patients should go to the hospital for examination in a timely manner, under the guidance of the doctor to use medication.