Abstract: OBJECTIVE To explore the correlation between vitamin D and severe pulmonary infection in children. METHODS Totally 41 children with severe pulmonary infection who were treated in the First Affiliated Hospital of Nanyang Medical College from Dec 2016 to May 2018 were assigned as the severe group, 40 children with common infection were chosen as the common group, and 40 children who received physical examination were set as the healthy group. The levels of white blood cell (WBC), procalcitonin (PCT), vitamin D, inflammatory factors interleukin-6 (IL-6), tumor necrosis factor -α(TNF-α), immune indexes CD₄⁺ and CD₈⁺ were observed and compared among the severe group, the common group and the healthy group at the time of suspected infection (T0), after infection for 24 hours (T1), after the infection for 48 hours (T2), after the infection for 72 hours (T3) and after the control of infection (T4). RESULTS The levels of WBC, PCT, IL-6 and TNF-α of the severe group and the common group were significantly higher than those of the healthy group at T0 (P<0.05). The levels of WBC, PCT, IL-6, TNF-α and CD₈⁺ of the children in the severe group and the common group, the children with sepsis and the children with severe sepsis were firstly elevated at T1, T2, T3 and T4 and then declined; the levels of above indexes of the severe group were significantly higher than those of the common group, and the levels of above indexes of the children with severe sepsis were significantly higher than those of the children with sepsis (P<0.05). The levels of vitamin D and CD₄⁺ of the children in the severe group and the common group, the children with severe sepsis and the children with sepsis were firstly reduced and then elevated; the levels of above indexes of the severe group were significantly lower than those of the common group; the levels of above indexes of the children with severe sepsis were significantly lower than those of the children with sepsis (P<0.05). Logistic analysis showed that IL-6 and TNF-α were associated with the severe pulmonary infection in the children, vitamin D and CD₄⁺/CD₈⁺ were protective factors. Vitamin D and CD₄⁺/CD₈⁺ were negatively correlated with WBC and PCT; IL-6 and TNF-α were positively correlated with WBC and PCT (P<0.05). CONCLUSION Vitamin D, IL-6, TNF-α and CD₄⁺/CD₈⁺ are associated with the severe pulmonary infection in the children. It is necessary to monitor the indexes so as to control the illness condition and reduce the risk of infection.