Abstract: OBJECTIVE To explore the distribution of respiratory tract flora in the neonates with infectious pneumonia and analyze the immunity of the neonates. METHODS From Mar 2016 to May 2018, totally 68 neonates who had hospital-associated infectious pneumonia were assigned a the study group and were divided into the mild group with 32 cases and the severe group with 36 cases according to the clinical pulmonary infection score during the hospital stay; meanwhile, 28 healthy neonates were set as the control group. The bacterial colony counts in target strip of sputum, richness, Shannon-Wiener diversity index, content of NK cell, cell subsets, vitamin D and expression of immunoglobulins were detected. RESULTS The positive rate of culture of respiratory tract bacteria was 60.29%(41/68) in the 68 neonates with infectious pneumonia. A total of 64 strains of pathogens were isolated, among which Acinetobacter baumannii combined with Acinetobacter acetate, Klebsiella pneumoniae and Enterobacter cloacae ranked the top 3 species. There were no significant differences in the number of target strips and Shannon-Wiener diversity index within 1 day of intubation or in 3-5 days of intubation; the number of strips and Shannon-Wiener diversity index of the severe group were less than those of the mild group, and there were significant difference (P<0.05). The levels of total NK and CD₃^-CD₅₆^negCD₁₆^bright of the study group were lower than those of the control group; the levels of CD₃^-CD₅₆^dimCD₁₆^bright and CD₃^-CD₅₆^brightCD₁₆^neg/dim of the study group were higher than those of the control group, and there was significantly difference in the CD₃^-CD₅₆^dimCD₁₆^brightbetween tow groups (P＜0.05) ,while there was no significantly difference in the CD₃^-CD₅₆^brightCD₁₆^neg/dim between tow groups. There were no significant differences in CD₃⁺CD₈⁺, CD₃⁺/CD₈⁺ and IgG between the study group and the control group; the levels of CD₃⁺ and CD₃⁺CD₄⁺ of the study group significantly were lower than those of the control group (P<0.05). CONCLUSION A. baumannii combined with A. acetate is dominant among the pathogens isolated from the neonates with infectious pneumonia, the number of NK cell and functional defect are prevalent among the neonates, and their cellular immune function is inhibited to varying degrees.