Bimaxillary protrusion is a kind of malocclusion, which is manifested by the simultaneous protrusion of the upper and lower jaws, which not only affects the aesthetics but also causes inconvenience to life. However, it is more common to see bimaxillary protrusion alone or bimaxillary protrusion with abnormal position of upper and lower jaws. So what are the factors that cause this disease? There are two main types: 1. Genetic factors: bimaxillary protrusion has a clear racial and familial predisposition. Studies have shown that the proportion of bimaxillary protrusion is highest among blacks and yellow people, lower among southern European whites and people from the Middle East, and lowest among northern European whites. The proportion of bimaxillary protrusion is higher in the southern part of the country than in the northern part. In addition, a significant proportion of patients with bimaxillary protrusion have similar deformities in blood relatives from one to three generations. A small number of patients with hereditary shortened upper lip, enlarged tongue, and oversized teeth can also show bimaxillary protrusion. 2. Environmental factors: nasopharyngeal obstructive diseases such as chronic rhinitis, adenoid hypertrophy, etc. affect the smooth flow of airways, gradually forming mouth whistling habits, some patients who may have been mildly Ann’s type III malocclusion show double premaxillary protrusion, but more for the upper dental arch narrowing, protrusion, Ann’s type II malocclusion. Some bad oral habits such as licking, improper use of musical instruments or lingual hypertrophy caused by systemic diseases may also cause the upper and lower incisors to tilt forward and manifest as bimaxillary protrusion. Early loss of upper and lower milk molars leads to anterior displacement of permanent molars, which may also cause anterior protrusion or crowding of upper and lower dental arches. In addition, the orthodontist may also cause anterior protrusion of the upper and lower dental arches and deterioration of the lateral facial appearance due to improper treatment planning or treatment measures, such as reluctant use of arch expansion treatment for moderate or moderate crowding cases, resulting in medically induced bimaxillary protrusion. In general, this disease has a great relationship with ethnicity and family genetics, and then some other diseases such as rhinitis also have a small chance to cause this deformity, which needs our attention.