Objective To evaluate the diagnostic and prognostic evaluation of Procalcitonin (PCT)levels detection for elderly patients with severe pulmonary infection.Methods 60 elderly patients with severe pulmonary infection were selected,as the infected group,wherein 45 cases with bacterial infection,15 cases with non -bacterial infections.Another 60 cases elderly patients excluded infectious diseases were selected as the control group.PCT,CRP and WBC levels in two groups were detected and compared.The infection group was randomly divided into two groups,each of 30 cases,the control group received conventional anti -infection treatment,while the observation group developed solutions to optimize antimicrobial drugs by detecting changes in PCT and CRP.Antibiotic course,antimi-crobial drug costs,superinfection and adverse reaction rates in two groups were recorded and compared.Results PCT,CRP levels and WBC in the infected group were (17.4 ±11.3)ng/mL,(43.5 ±18.7)mg/L and (10.4 ± 7.3)×109 /L,which in the control group were (0.4 ±0.2)ng/mL,(6.3 ±3.6)mg/L and (5.4 ±1.4)×109 /L,the difference was statistically significance (t =7.369,9.570,3.295,all P <0.05 ).PCT levels of bacterial infection group was (27.2 ±14.7)ng/mL,which in non -bacterial infection group was (8.2 ±2.7)ng/mL,the difference was statistically significant (t =7.369,9.570,3.295,all P <0.05).Antibiotic course,antimicrobial drug costs,superin-fection and adverse reactions in the observation group were significantly lower than those in the control group,the difference statistically significant (t =6.994,27.71,χ2 =6.171,6.984,all P <0.05).Conclusion PCT detection has an important value of infection diagnosis especially in elderly patients with severe pulmonary infection,and can be used as the basis for antibiotic treatment.