Mouth breathing is one of the most common oral and maxillofacial abnormalities in children. Children with mouth breathing are often accompanied by obstructive sleep apnea, which not only affects children's dentofacial development, leading to the occurrence of malocclusion, but also may lead to a series of serious systemic complications. The diagnosis and treatment of mouth breathing and its related malocclusions require multidisciplinary collaboration. This paper discusses the etiology and harm of mouth breathing, diagnosis of mouth breathing related problems, correlation between mouth breathing and malocclusion, treatment of mouth breathing related malocclusions.