Objective To investigate the application effect of bronchoalveolar lavage (BAL) in children with severe Mycoplasma pneumoniae pneumonia (SMPP).Methods A total of 80 children with SMPP admitted to the Department of Respiratory,Fujian children's Hospital from August 2020 to August 2021 were selected as the research subjects.They were divided into control group and study group according to the random number table method with 40 cases in each group.The control group was given routine anti infection treatment,and the study group was given bronchoalveolar lavage on the basis of the control group.The therapeutic effect,improvement of symptoms and signs,pulmonary function indexes and adverse reactions were compared between the two groups.Results The total effective rate of the study group was higher than that of the control group,with a statistically significant difference (P＜0.05).The improvement rate of chest X-ray in the study group was higher than that in the control group,with a statistically significant difference (P ＜0.05).The time of fever abatement and hospitalization in the study group were shorter than those in the control group,with statistically significant differences (P＜0.05).The forced vital capacity,forced expiratory volume in one second,peak expiratory flow in the study group were higher than those in the control group,and the differences were statistically significant (P＜0.05).The total adverse reaction rate of the study group was lower than that of the control group,with a statistically significant difference(P＜0.05).Conclusion The application of bronchoalveolar lavage in SMPP has a significant effect,which can significantly improve the clinical symptoms of patients,improve lung function indicators,and reduce the incidence of adverse reactions.It has positive clinical significance and is worth recommending and using.