When children have cavities in big teeth, the depth of cavities can be probed and the treatment measures can be taken after pulp vitality test, as follows: i. If the cavity of milk teeth is not deep, it can be repaired by using glass ion cementum etc. after removing the decaying matter. If the cavity area of milk molar is large, it can be prepared to dove tail cementation shape, and then apply silver amalgam to fill the adjacent surface and jaw surface respectively, pay attention to form good adjacent relationship to prevent the occurrence of food embedment. If the X-rays show that the pulp of the milk molar is exposed in the cavity and produces pulpitis or periapical inflammation, the pulp cavity can be ground open under local anesthesia, the infected pulp can be removed, the root canal can be filled with calcium hydroxide paste, and the cavity can be closed finally. If the molar forms residual root and crown, the prognosis is poor, it can be extracted and wear a gap retainer.