Objective To study the expression and clinical significance of serum sialic acid and C3 in children with mycoplasma pneumonia and airway mucus plug. Methods 206 children with mycoplasma pneumonia (MPP) who were diagnosed and treated in our hospital from March 2017 to March 2018 were selected as the research objects. According to the results of bronchoscopy, children with MPP were divided into MPP alone group (130 cases) and MPP with mucus suppository group (76 cases). The levels of serum sialic acid and complement C3 in each group were detected, and the differences in serum sialic acid and C3 levels in each group were statistically analyzed and compared. Receiver operating curve analysis (ROC) were used to analyze the value of serum sialic acid and C3 levels in the diagnosis of MPP combined with airway mucus plugs. Univariate and multivariate COX regression analysis were used to analyze the influencing risk factors of mycoplasma pneumonia complicated with airway mucus embolism.Results Compared with the simple MPP group, the serum sialic acid and C3 levels of the MPP combined with airway mucus suppository group were significantly higher before treatment, and the difference was statistically significant (P＜0.05). ROC curve analysis results show that serum sialic acid, C3 and the combined detection of AUC were 0.705, 0.631 and 0.786, respectively. The combined detection of MPP with airway mucus plugs has a significantly higher diagnostic value than a single index (P＜0.05). Univariate and multivariate COX regression analysis found that age＞5 years old, atelectasis, serum sialic acid＞86. 23mg/L and serum C3＞1.35g/L are independent risk factors for airway mucus thrombosis in children with MPP.Conclusion The levels of serum sialic acid and complement C3 in children with MPP complicated with airway mucus embolism are elevated, age＞ 5 years old, atelectasis, serum sialic acid＞86.23 mg/L and serum C3＞1.35 g/L are independent risk factors for MPP with airway mucus, the detection of serum sialic acid and complement C3 levels is helpful for the early diagnosis of MPP combined with airway mucous embolism.