Abstract：Objective To analyze the changes of immune function in infants with cytomegalovirus pneumonia and understanding of the pathogenesis of the disease. Methods A total of 36 infants diagnosed with cytomegalovirus pneumonia at Wuchang Hospital and Pure Ren Hospital affiliated with Wuhan University of Science and Technology from September 2018 to January 2020 were selected as the experimental group, and 36 healthy infants in the same period were selected as the control group. The levels of serum immunoglobulins, including IgG, IgA, IgM, and complements C3, C4, were compared between the two groups using the nephelometry method. The expression rates of peripheral blood CD3+ total T lymphocytes, CD4+ T lymphocytes, CD8+ T lymphocytes, the ratio of CD4+/CD8+ T lymphocytes, and NK cells were detected by flow cytometry. Results There was no significant statistical difference in serum immunoglobulins and complement levels between the two groups （t＝1.981, 1.133, 0.796, 0.173, 1.219, all P＞0.05）; the expression rates of CD3+ total T lymphocytes, CD4+ T lymphocytes, CD4+/CD8+ T lymphocyte ratio, and NK cells in the experimental group were significantly lower than those in the control group, while the ratio of CD8+ T lymphocytes was higher in the experimental group, with significant differences between the two groups （t＝4.232, 2.135, 3.515, 5.411, 2.705, all P＜0.05）. Conclusion Cellular immune response plays an important role in the occurrence and development of infant cytomegalovirus pneumonia infection. Focusing on immune regulation in affected infants may become a new approach in clinical diagnosis and treatment.