Abstract: Objective Pneumonia in children is a common inflammatory disease of the respiratory system and the most common cause of death in children under 5 years worldwide. Exploring the key genes and pathways of early diagnosis of pneumonia in children is of great significance for studying the pathogenesis of pneumonia. 
Methods The dataset was screened from Gene Expression Omnibus (GEO) database, and differentially expressed genes were screened by GEO2R. Key genes and core genes of DEGs were analyzed and screened. Finally, the receiver operating characteristic (ROC) curve analysis was conducted using GSE42834 dataset. 
Results A total of 375 DEGs were obtained, of which 96 were up-regulated and 279 were down-regulated. Geneontology (GO) analysis revealed that DEGs were mainly enriched in immune effector process, cell activation, cell secretion, immune molecule binding, and complement receptor activity. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis suggested that DEGs were mainly enriched in immune and infectious disease pathways. The top 5 key genes were identified through Protein Protein Interaction (PPI) analysis, namely HLA-A, MAPK14, CD8A, HIST2H2AC, and IL2RB. The areas under ROC curve of MAPK14, CD8A, HIST2H2AC and IL2RB were all greater than 0.7, which showed good diagnostic value. Further analysis suggested that IL2RB might be the core gene involved in the pathogenesis of pneumonia by regulating the JAK-STAT signaling pathway. 
Conclusion HLA-A, MAPK14, CD8A, HIST2H2AC and IL2RB are key genes for early diagnosis of pneumonia in children. IL2RB, the core gene, participates in the pathogenesis of pneumonia in children by regulating the JAK-STAT signaling pathway.

Key words: pneumonia, gene expression； child