Whether the root canal treatment for four-year-old children is painful or not is related to the specific situation, as follows: 1.No pain will be produced: If the large area of decay of the milk tooth causes chronic infection of the pulp and leads to pulp necrosis and the formation of gingival fistula or sinus tract, the pulp tissue has lost its vitality, and no pain will be produced during the process of removing the pulp for root canal preparation. 2.With pain: When the milk tooth is fractured by trauma and the fresh pulp is exposed When the pulp is exposed to hot or cold stimulation, it can produce obvious pain, and the pulp can be removed under local anesthesia to complete root canal treatment. When acute pulpitis or periapical inflammation occurs in a baby tooth, the pulp tissue is partially alive, and direct removal of the pulp tissue may produce sharp pain, which needs to be combined with endodontic anesthesia to completely remove the remaining pulp and finally complete the root canal treatment.