Purpose:Study the clinical significance of dynamic monitoring of serum calcitonin original for elderly patients with severe pneumonia in ICU.Methods:78 cases of elderly patients with severe pneumonia selected in our hospital ICU,according to the prognosis after treatment can be divided into survival group A and group B death,and we need comparing two sets of biochemical index and risk of death Conclusion:Calcitonin original level in group A appear progressive decline and group B calcitonin original progressive rise,but the two groups of patients do not have obvious difference between white blood cellcount,percentage of neutrophils and hypersensitive c-reactive protein levels.5th and 7th days,the death risk of B group was obviously higher than that of group A.Conclusion:Dynamic detection of serum calcitonin original can effectively judge the severity of elderly patients with severe pneumoniain the ICU and assessment of prognosis,with high sensitivity,strong specificity.