Objective To study the effect of lip muscle function training for children with oral breathing during orthodontic treatment period and its effect on dental and maxillofacial development. Methods A total of 88 children with oral breathing who received orthodontic treatment in the First People's Hospital of Changzhou/the Third Affiliated Hospital of Soochow University from January 2022 to October 2023 were selected and divided into control group and observation group according to the random number table method, with 44 children in each group. The control group received routine intervention, and the observation group received lip muscle function training on this basis. The oral morphological indexes (ANB angle, SNB angle, NP-FH angle, U1-NA angle) and maxillofacial morphological changes (nasolabial angle, chin-labial angle, chin-neck angle and facial angle), comfort and aesthetics were compared between the two groups. Results After correction, the ANB angle, U1-NA angle and SNB angle of the observation group were smaller than those of the control group, and the NP-FH angle was larger than that of the control group (P<0.05). The facial angle of the observation group was smaller than that of the control group, and the chin-neck angle, chin-lip angle and nasolabial angle were larger than those of the control group (P<0.05). The scores of comfort and aesthetics in the observation group were higher than those in the control group (P<0.05). Conclusion Lip muscle function training can promote the recovery of oral morphology and maxillofacial morphology, improve comfort and aesthetics, and can be used as a supplementary intervention for orthodontic treatment in children with oral breathing during orthodontic treatment.