A 3 year old child with severe tooth decay (clinically known as caries) should be treated with caries filling, root canal therapy or tooth extraction. 1. If tooth decay caused by dental caries does not erode the pulp tissue, i.e., there is no symptom of pulpitis such as hot/cold pain, spontaneous pain or biting pain; caries filling can be carried out, i.e., the decayed tooth tissue is ground clean, and the defective part can be repaired by filling materials (e.g., tooth powder, resin). 2. If the caries has caused pulp infection and symptoms of pulpitis, root canal treatment is necessary to remove the necrotic and inflamed pulp tissue to effectively cure the above symptoms. 3. If the decay is so severe that the tooth cannot be retained by caries filling or root canal treatment, it should be extracted in time and the gap should be maintained after the wound has healed. It is recommended that a 3 year old child with severe tooth decay should seek medical attention for symptomatic treatment in time to avoid delaying the condition.