Bilateral facial asymmetry may be caused by congenital or acquired factors. Such as the first and second branchial arch syndrome, hemifacial corpuscles, hemifacial atrophy or hemifacial hypertrophy, unilateral trauma or infection, long-term unilateral chewing habits, etc. It has been proved that most asymmetries are caused by acquired environmental factors. Among them, the habit of unilateral chewing is the first, and the left chewing is the most. In recent years, the research on bilateral facial asymmetry shows that from the period of mixed dentition to the early permanent dentition, even the permanent dentition, mandibular displacement first occurs, and then it evolves into skeletal dysplasia, and the degree of abnormality is from less to more, which makes bilateral facial asymmetry show an obvious trend of increasing with age. If people born by congenital factors, in addition to asymmetric deformity, often have the characteristics of tooth deformity. Then, those who suffer from acquired factors-long-term unilateral chewing habits will be highlighted as swelling of the external mandibular angle on the unilateral chewing side, accompanied by hypertrophy of masticatory muscles; The nasolabial groove of this side is deepened, the height of 1/3 in the plane is obviously reduced, and the chin junction is also offset to this side. On the contrary, the opposite half face is flat, subcutaneous fat accumulates, and the soft tissue in infraorbital region is plump. The degree of asymmetry deformity is especially serious in childhood, especially in the rapid growth period. As for the causes of unilateral chewing, the most common one was that one side was often painful and inflamed due to dental caries, which led to unilateral disuse and long-term use of contralateral chewing. There are also many people who chew unilaterally because of one canine tooth or poor filling. At present, due to the development of stomatology, especially the prevention and treatment of dental caries in the whole people, the incidence of dental caries has decreased significantly, so that the main cause of unilateral chewing is not the same as before, and the rise of dental occlusion disorder is the main inducing cause. Therefore, it is of great significance to emphasize the corresponding orthodontic treatment, especially early treatment, to prevent unilateral chewing. At present, with the progress of stomatology, new concepts of preventive correction and blocking correction have been put forward. The so-called preventive correction refers to finding the factors that affect normal growth and development, maintaining normal occlusion and preventing malocclusion. Occlusal correction means that in addition to eliminating the cause in time, it is also necessary to interrupt the previously discovered or developing (occlusion) deformity in time and rebuild the normal (occlusion). If you really do this, it will get twice the result with half the effort to prevent bilateral facial asymmetry.