Objective To investigate the value of secretory leukocyte protease inhibitor（SLPI）in serum and lower respiratory tract secretion in severe pneumonia. Methods 90 patients with severe pneumonia from the Intensive Care Unit（ICU）of the Third People′s Hospital of Hefei were selected for clinical data. They were respectively divided into a survival group and a death group based on their28⁃day survival status. Baseline data，serum and lower respiratory tract secretions（SLPI）and serum Tumor necrosis factor⁃α（TNF⁃α），Interleukin⁃8（IL⁃8）levels were compared between the two groups at admission to ICU and after 24 hours treatment.Analyzing the correlation between serum SLPI and lower respiratory secretions SLPI，TNF ⁃ αand IL ⁃8. Conduct binary logistic regression analysis on the influencing factors of prognosis for severe pneumonia. And used receiver operating characteristic （ROC）curve to analysis the evaluation value of patient serum and lower respiratory tract secretions（SLPI）for the prognosis of severe pneumonia. Results The mechanical ventilation time in the death group was longer than that in the survival group，and there was no significant difference in the remaining baseline data（P > 0.05）. After 24 hours of treatment，the serum and lower respiratory tract secretion SLPI of both groups increased compared to before，and serum TNF⁃α，IL⁃8 levels decreased（P < 0.05）. After treatment，the SLPI of serum and lower respira⁃ tory tract secretions in survival group were higher than those in the death group，and the serum TNF⁃α，IL⁃8 levels were lower than those in the death group（P < 0.05）. Spearman correlation analysis found that serum SLPI and TNF⁃ α，IL⁃8 showed a negative correlation（r = -0.583，-0.672，P < 0.001）；And there was a positive correlation with lower respiratory tract secretion SLPI（r = 0.527，P < 0.001）. The binary logistic regression analysis showed that serum and lower respiratory tract secretions（SLPI）were protective factors for 28 day mortality in severe pneumonia （P < 0.05）. ROC curve analysis showed that the area under the curve（AUC）of serum and lower respiratory secretion SLPI after treatment were 0.953 and 0.968. Patients with serum SLPI < 87.59 ng/mL and lower respiratory secretion SLPI < 835.68 ng/mL had poor prognosis（P < 0.05）；The combined prediction efficiency of the two indicators is higher than that of individual indicators，with an AUC of 0.991（P < 0.05）. Conclusion SLPI is a protective factor in severe pneumonia，serum and lower respiratory tract secretions SLPI may serve as effective indicators for the treat⁃ ment and predictive evaluation of severe pneumonia.