Objective To investigate the effect of orbicularis oris muscle function training on dento-maxillofacial development in mouth breathing children during orthodontics period. Methods A total of 56 children with mouth breathing admitted to our hospital from January 2022 to July 2023 were selected and randomly divided into control group and observation group, with 28 children in each group. The control group was only treated with conventional orthodontics, and the observation group was treated with systematic orbicularis oris muscle function training on the basis of the control group at 3 months after operation. The dental cephalometric measurement indexes, facial angle measurement indexes and satisfaction were compared between the two groups. Results The indexes of U1-SN and L1-MP in the observation group were better than those in the control group (P <0.05). There was no significant difference in OP-FH index between the two groups (P >0.05). After treatment, the nasolabial angle, chin-lip angle, chin-neck angle and facial angle in the observation group were better than those in the control group (P <0.05). The satisfaction rate in the observation group was 96.43%, which was higher than 71.43% in the control group (P <0.05). Conclusion Orbicularis oris muscle function training can effectively improve the development of oral and maxillofacial region in children, showing good improvement in dental cephalometric indexes such as U1-SN and L1-MP, as well as nasolabial angle, chin-lip angle and facial angle, with high satisfaction. It has high clinical application value.