Objective: To study the clinical effect of bronchoalveolar lavage (BAL) combined with vibration expectoration in the treatment of children with severe pneumonia undergoing mechanical ventilation. Methods: From February 2018 to January 2020, 120 children with severe pneumonia receiving mechanical ventilation in the pediatric intensive care unit (PICU) of Deyang People’s Hospital were selected. The children were randomly divided into a BAL group and a combined group, with 60 cases in each group. All the children received symptomatic treatment such as anti-infection, expectoration, and cough relieving. The children in the BAL group were given BAL treatment, and vital signs were closely monitored during lavage; the children in the combined group were given bronchoalveolar lavage combined with high-frequency vibration expectoration treatment, which was performed 20 minutes before BAL treatment. The changes of respiratory function and inflammatory factors before and after BAL treatment were observed. The sputum output, mechanical ventilation time, PICU hospital stay, 28-day mortality, and clinical efficacy were compared between the 2 groups. Results: After 2 hours of treatment for both groups, oxygenation index (PaO2/FiO2) and dynamic compliance (Cydn) were significantly increased, partial pressure of carbon dioxide (PaCO2) was significantly decreased (P<0.05); the above indexes in the combined group were significantly improved than those in the BAL group (P<0.05). After 5 days of treatment, serum procalcitonin (PCT), C-reactive protein (CRP), and white blood cell (WBC) in the 2 groups were significantly lower than those before the treatment (P<0.05); the levels of serum PCT and CRP in the combined group were significantly lower than those in the BAL group (P<0.05). The sputum excretion volume of BAL in the combined group was more than that in the BAL group and the mechanical ventilation time and PICU hospitalization time were shorter than those in the BAL group (P<0.05). However, there was no significant difference in 28-day mortality between the 2 groups (P>0.05). After the treatment, the total effective rate of the combined group was 96.67%, which was significantly higher than that of the BAL group (85.00%, P<0.05). Conclusion: BAL combined with vibration expectoration can help children with severe pneumonia fully expectorate, improve respiratory function, reduce inflammatory reaction, shorten mechanical ventilation time and PICU hospitalization time, and increase clinical efficacy.