Pus in the gums after a toothache is usually caused by apical periodontitis, which needs to be treated by incision and drainage of pus, as well as opening of the pulp cavity and root canal treatment, in order to eliminate the pus and inflammation, and relieve the pain, as follows. When the inflammation is located in the periapical tissues, the chemical action of inflammatory substances and the increase of local tissue tension due to inflammatory exudation will cause toothache, and when the pus is formed and develops to the subperiosteal or submucosal stage, the pus bag can appear on the gum. The abscess should be incised and drained under local anesthesia, and if the abscess is deeply located, a rubber drainage strip may be placed and changed once a day until it is withdrawn in the absence of pus. Medullary cavity opening is usually performed at the same time, which helps to drain the exudate, reduce pressure and relieve pain. Root canal therapy is then performed to completely eliminate inflammation in the root canal and periapical area. There may be other reasons for the appearance of pus in the gums after a toothache, and it is recommended to visit the hospital for early and proper treatment.