Functional orthodontic appliances are mainly applied to functional malocclusion caused by abnormal function of orofacial muscles. In addition, early bony malocclusion can also be used when it promotes normal orofacial functional activities and provides a favorable environment for craniofacial skeletal and dental development; functional orthodontic appliances are best suited to be started 1-2 years before youthful growth and eruption and continue throughout the eruption period. For Chinese children, females enter the eruption period at an average age of 9-10 years and males at an average age of 12-13 years. Considering the age of the teeth, functional orthodontic appliances are mainly used for patients in the replacement period, but they can also be used in the period of milk teeth and early permanent teeth. When facial growth is nearly complete, their efficacy is significantly limited. Functional orthodontic appliances are mainly used for the correction of length disproportion, both for Anser II class wrong (dentition) and Anser III class wrong (dentition); wrong (dentition) functional orthodontic appliances can also be used for the correction of height disproportion, which is more effective for deep overdentures (dentition), as well as for open dentition. In addition, functional orthodontic appliances can be used for height disproportion in posterior teeth, but are not suitable for crowded teeth, misaligned teeth and extraction cases. Functional appliances can be used in conjunction with mechanical appliances to align teeth if needed.