Objective To investigate the clinical effectiveness of oral appliances in the treatment of mouth breathing in children and analyze the differences in clinical outcomes between different types of oral appliances. Methods PubMed, EMbase, The Cochrane Library, China Knowledge, Wanfang database, Wipro Chinese Journal Service platform and other databases were used to search for clinical studies on oral appliances for the treatment of oral respiration in children, and the methodological quality of the included literature was evaluated by the Cochrane Risk of Bias Assessment Tool. The RevMan 5.4.1 software was used to analyse of the included data. A total of 13 papers with 245 patients were included in this study and analyzed for upper alveolar seat angle (Sella nasion A point angle, ∠SNA), upper and lower alveolar seat angle (AN plane angle, ∠ANB), lower alveolar seat angle (Sella nasion B point angle, ∠SNB), oropharyngeal minimum cross-sectional area, and distance from hyoid bone to cervical vertebra 3 (H-C3) were meta-analyzed. Results Meta-analysis showed that eight papers reported that oral appliances had no effect on ∠SNA in mouth-breathing children; nine papers reported that oral appliances decreased ∠ANB in mouth-breathing children. Ten papers reported that oral appliances increased ∠SNB in mouth-breathing children; two papers reported that oral appliances increased oropharyngeal minimum cross-sectional area; two papers reported that oral appliances increased H-C3. Seven papers literature reported that oral appliances significantly decreased U1-SN; and except for ∠SNA, oropharyngeal minimum cross-sectional area, and U1-SN. There was heterogeneity in the data reported in the literature for all other observables. According to the type of oral appliance used, the group was divided into 2 subgroups, the MRC myofunctional orthodontic group and the other orthodontic group, and subgroup analyses were performed, which showed that heterogeneity still existed within the 2 subgroups in terms of ∠ANB and ∠SNB, but there was no heterogeneity between the ∠ANB subgroups, and there was heterogeneity between the ∠SNB subgroups. Conclusion Oral appliances can play an important role in the correction of mouth breathing in children by adjusting the position of the jaw in relation to the cranium