Gum fistula after root canal treatment is considered to be a localized infection, which may also be related to chronic apical periodontitis. 1. Localized infection, if there is invasion of bacterial virus or other pathogens after root canal treatment for gingival fistula, it may lead to suppurative infection, so a small bubble of rice grains will appear. 2. Chronic periapical inflammation, if the root canal treatment is not complete after root canal treatment, it is easier to induce chronic periapical inflammation after a long time, chronic periapical inflammation produces tissue fluid exudation, the formation of abscesses, so this symptom will appear. Usually need to regular medical examination, if found abnormal symptoms, it is best to timely medical treatment, so as not to have an impact on the recovery of the body.