〔Abstract〕Objective To explore the effect of gamma globulin in the treatment of severe mycoplasma pneumoniae pneumonia (SMPP) in children. Methods A total of 120 children with SMPP admitted to Zhongshan People’s Hospital from December 2018 to December 2019 were randomly divided into a control group (60 cases) and an observation group (60 cases). The control group was treated with azithromycin and the observation group was treated with gamma globulin on the basis of the control group. The clinical efficacy, time of symptom improvement, and lung function indexes were compared between the two groups of children. Results The effective rate of clinical treatment in children in the observation group was 93.33%, which was higher than 80.00% in the control group. The difference was statistically significant (P < 0.05); Time of fever regression, lung rale disappearance time, and cough stop time were all were shorter than those of the control group, and the differences were statistically significant (P < 0.05); After treatment, the two groups of children increased their forced expiratory volume (FEV1), forced vital capacity (FVC), and FEV1/FVC in the first second compared to those before treatment, and the lung function indexes in the observation group is higher than those in the control group, the differences were statistically significant (P < 0.05). Conclusion Gamma globulin has a significant clinical effect in adjuvant SMPP, which can shorten the recovery time of children and effectively improve the lung function of children.