Objective To analyze the neutrophil to lymphocyte ratio (NLR)'s prognostic value in patients with prognosis of severe pulmonary infection in intensive care unit (ICU). Methods A total of 102 severe patients who were treated in our hospital for pulmonary infection from May 2020 to May 2022 were selected as the research subjects. According to the survival status of the patients on day 28 after treatment, they were divided into a control group (patients who survived on day 28 after treatment, n=51) and a study group (patients who died within 28 days after treatment, n=51). The risk factors affecting the prognosis of severe pulmonary infection patients were determined by Logistic regression analysis, established the prediction score model, and evaluated the model. Logistic regression, restricted cubic spline model and clinical decision (DCA) curve were used to evaluate the clinical prognostic value of dimensional NLR in ICU patients with severe pulmonary infection.Results Duration of heating ＞7 d, length of hospital stay ＞7 d, body temperature, lactate dehydrogenase (LDH), vitamin D, interleukin-6 (IL-6), interferon-γ (IFN-γ) and pulmonary consolidation were independent risk factor for predicting severe lung infection(P＜0.05).The best cut-off values before and after validation were 4.25 points. The evaluation results show that the predictive scoring model had high accuracy, good effectiveness, safety and reliability, and strong practicability. The intensity of the association between the continuous change of NLR and the occurrence of prognosis of severe pulmonary infection was nonlinear dose-response relationship (P＜0.01). There was a significant positive correlation between NLR and severe pulmonary infection, especially when the NLR＞50, with the increase of NLR, the incidence of prognosis of severe pulmonary infection increased significantly. The results of DCA curve analysis showed that NLR had important clinical value in predicting severe pulmonary infection. Conclusion The independent risk factor for severe pulmonary infection is NLR, and the correlation between NLR and prognosis of severe pulmonary infection is a nonlinear dose response relationship