The orthodontic treatment of malocclusion has a certain relationship with age, and each dental age has its indications for orthodontic treatment, which means that different malocclusions should be treated at different ages. Crowding, a common malocclusion, is generally not treated at the beginning of the tooth replacement period. Because the teeth are being replaced, the jawbone is developing, the severity of crowding cannot be best determined, and it is difficult to determine whether or not tooth extraction should be performed. Even if the extraction orthodontic treatment should be carried out, the extracted teeth may not have erupted yet, so crowded teeth generally have to wait until all the milk teeth are replaced before starting orthodontic treatment. In addition, some malocclusions, such as anterior retrusion, should be corrected as early as possible to avoid affecting the normal development of the jaws. Early osseous malocclusion should also be treated during the period of dentition or even the period of milk teeth to control the growth of the jaws. Some serious bony malocclusion with obvious genetic tendency can wait until the jaws are mature to be orthodontically and surgically combined to achieve a more satisfactory and stable result. In conclusion, the best period of orthodontic treatment differs for different malocclusions, so it is best for patients with malocclusion to see an orthodontic specialist first to clarify the type of malocclusion and to determine the best period of orthodontic treatment.