〔Abstract〕 Adenoid hypertrophy is a common respiratory disease in children. It is usually caused by infection and other inflammatory stimulis, leading to pathological hyperplasia and hypertrophy of the adenoids in children. Clinical symptoms are often accompanied by nasal congestion, snoring, mouth breathing and other respiratory changes, resulting in children's maxillofacial malformation, adenoid facial appearance, and obstructive sleep apnea syndrome (OSAS), sudden infant death syndrome (SIDS) and other complications. Adenoid hypertrophy is considered to be the main cause of mouth breathing in children. Adenoid hypertrophy causes airway blockage and children are forced to adopt the breathing position with head held high and mouth breathing. In recent years, studies have found that there is a strong correlation between mouth breathing and malocclusion caused by adenoid hypertrophy. This article reviews the research progress of mouth breathing and malocclusion caused by adenoid hypertrophy as well as the treatment methods.