Abstract: Objective To explore the diagnostic value of the change rate of lactate and procalcitonin in severe pneumonia patients. Methods From January 2017 to January 2018, 124 patients with severe pneumonia treated in our hospital were collected, and the patients were divided into death group (n=32) and survival group (n=92) according to whether the patients died within the hospital or not. The clinical characteristics of the two groups were observed, and the change rates of lactate and procalcitonin were observed. Results When compared with the survival group, the lactic acid, lactate rate, procalcitonin, procalcitonin and APPACHE II scores in the death group increased significantly (P<0.05). There was no statistical difference between the two groups in C reactive protein (P>0.05). In the value of diagnosis of death in severe pneumonia patients, the area in the ROC curve from high to low was the rate of calcitonin change rate, APPACHE II, lactic acid change rate, calcitonin, lactic acid and C reactive protein, respectively. The change rate of procalcitonin and lactate were 0.966 (0.942-0.989) and 0.782 (0.702-0.859) respectively. Conclusion The change rate of lactate and the change rate of procalcitonin have a good specificity and sensitivity in the diagnosis of poor prognosis in patients with severe pneumonia.