Objective <p>Some studies propose that asthma is a clinical complication of mycoplasma pneumoniae pneumonia (MPP). This study explored the role of Th17/Treg immune balance in assessing disease severity in children with MPP and analyzed its ability to distinguish asthma complications in MPP.</p> Methods <p>MPP children (<i>n</i> = 249) and healthy children as controls (<i>n</i> = 120) were enrolled. General baseline data were collected. Th17 and Treg cells were detected, and the Th17/Treg ratio was calculated. IL-17/IL-6/IL-10/TGF-β1 levels were assessed. A logistic regression model was established, and an ROC curve was plotted.</p> Results <p>The proportion of peripheral blood Th17 cells, serum IL-17 and IL-6, and the Th17/Treg ratio were higher, while the proportion of Treg cells and serum IL-10 and TGF-β1 were lower in children with MPP. The Th17/Treg imbalance was more pronounced in severe MPP than in mild MPP. The Th17/Treg ratio had an AUC of 0.845 for predicting severe MPP. Children with severe MPP complicated by asthma exhibited higher serum IL-17 and Th17/Treg ratios compared to those without asthma; their Treg cell proportion and serum IL-10 levels were lower. The AUC of the combined detection of the Th17/Treg ratio, serum IL-17, and serum IL-10 for distinguishing severe MPP children with or without asthma was 0.823, which was significantly higher than that of serum IL-17 or IL-10 alone. An elevated Th17/Treg ratio was an independent risk factor for asthma in severe MPP.</p> Conclusion <p>Children with MPP complicated by asthma exhibit more severe disease, characterized by exacerbated peripheral blood Th17/Treg immune imbalance. Combined assessment of the Th17/Treg ratio, IL-17, and IL-10 aids in distinguishing whether severe MPP patients have comorbid asthma.</p>