Objective To investigate the expression and clinical significance of phosphatidylinoinosidine­3­ kinase （PI3K） and matrix metalloproteinase 9（MMP­9） in bronchoscopic alveolar lavage fluid of children with severe pneumonia in pediatric intensive care unit （PICU）. Methods A total of 103 children with severe pneumonia admitted to PICU of the hospital from January 2021 to June 2022 were enrolled. All patients underwent fiberbronchoscopic alveolar lavage. Real­time fluorescence quantitative polymerase chain reaction was used to determine the expression of PI3K， and enzyme­linked immunosorption was used to determine the expression of MMP­9 in alveolar lavage fluid. The patients were followed up for 21 days after admission to evaluate the prognosis. Logistic regression analysis was used to analyze the factors affecting the prognosis. Pearson correlation was used to analyze the correlation between the expression levels of PI3K and MMP­9 in the bubble lavage solution and the child Critical Case Score （PCIS） and child Organ Dysfunction 2（PELOD­2） Scores. The values of PI3K and MMP­9 expression levels in alveolar lavage fluid to predict the prognosis were analyzed by receiver operating curve （ROC）. Results Among the 103 children，29 cases had poor prognosis vs 74 cases had good prognosis. Logistic multivariate regression analysis showed that combined shock （OR = 4.104，95%CI：1.689 ~ 9.974）， PELOD­2 score （OR = 4.764，95%CI：1.960 ~ 11.577）， PCIS score （OR = 5.068，95%CI：2.085 ~ 12.318）， PI3K （OR = 3.924，95%CI：1.614 ~ 9.536） and MMP­9 （OR = 3.873，95%CI：1.594 ~ 9.412） were the prognostic factors of PICU children with severe pneumonia （P < 0.05）. Pearson correlation analysis showed that the expression levels of PI3K and MMP­9 in alveolar lavage fluid were negatively correlated with PCIS scores （r = -0.598，P = 0.000；r = -0.537，P = 0.000）， PI3K and MMP­9 expression levels in alveolar lavage fluid were positively correlated with PELOD­2 scores （r = 0.546，P = 0.000；r = 0.571，P = 0.000）. ROC curve results showed that the sensitivity of PI3K， MMP­9 and their combination to predict the prognosis of PICU children with severe pneumonia was 75.86% （95%CI：56.08% ~ 88.98%），72.41% （95%CI：52.51% ~ 86.55%） and 82.76% （95%CI：63.51% ~ 93.47%）， the specificity was 75.68% （95%CI：64.07% ~ 84.58%）， 79.73% （95%CI：68.47% ~ 87.85%），89.19% （95%CI：79.28% ~ 94.88%）， and the AUC was 0.762（95%CI：0.666 ~ 0.859），0.767（95%CI：0.670 ~ 0.873），0.909（95%CI：0.848 ~ 0.971）. Conclusion The expression of PI3K and MMP­9 in bronchoscopic alveolar lavage fluid was related to the prognosis of children with severe pneumonia in PICU， and the combination in predicting the prognosis was effective， so it has certain clinical value to use them as a sensitive indicator to predict the prognosis of children with severe pneumonia in PICU.