Four-year-old baby incisor caries can be treated separately according to the specific situation, as follows: First, if shallow cavity is formed on the adjacent surface of incisor, the decayed tooth tissue can be abraded from the lingual surface and the composite resin with strong adhesive is applied to fill it, pay attention to remove the extra material to prevent stimulating the redness and swelling of the gum. If the cavity is close to the pulp angle, the defect can be repaired after placing calcium hydroxide cushion at the bottom of the cavity. If the incisor surface forms extensive caries, the filling material cannot be fixed, resin preformed crown can be made to repair. If the cavity of incisor is deeper and causes pulpitis or periapical inflammation, causing obvious pain, the cavity can be filled after grinding open the pulp cavity under local anesthesia, removing the infected pulp and applying iodoform paste to seal the root canal.