【Abstract】 Objective To investigate the correlation of plasma copeptin and illness severity and prognosis in children with severe pneumonia. Methods 225 patients with pneumonia and 80 healthy children in our hospital from Jan. 2015 to Jan. 2016 were selected as the study objects. They were retrospectively analyzed and divided into severe pneumonia children (103 cases) and common pneumonia children (122 cases). The severe pneumonia children were divided into death group (10 cases) and survival group (93 cases). The gender, age, plasma Copeptin, CRP and PCT indexes of patients were recorded. The differences of the above data were compared. The sensitivity and specificity of different clinical indexes in the evaluation of illness severity, prognosis were analyzed. Results The levels of plasma copeptin, CRP, PCT, WBC and NEU percentage in severe pneumonia children and common pneumonia children were significantly higher than those in normal children. The severe pneumonia children had higher levels of plasma Copeptin, CRP, PCT, the difference was statistic significant （P＜0.05）. The levels of plasma copeptin, CRP, PCT in died children were significantly higher than those in survival children （P＜0.05）, but there was no statistic significance in the WBC level and NEU percentage between the two groups（P＞0.05）. The nonconditional Logistic regression analysis showed that, higher levels of plasma copeptin, CRP, PCT were independent risk factors of severe pneumonia （P＜0.05）. The higher copeptin level, the larger influence was. Conclusion The serum copeptin level in severe pneumonia children is significantly higher than that in common pneumonia children and normal physical examinees. With the aggravated illness condition, the serum copeptin level increased gradually. The serum copeptin combined with CRP and PCT are independent risk factors of death in severe pneumonia children, and which can be seen as one of the effective indexes in the prognosis in severe pneumonia children.