To explore the value of procalcitonin and its dynamic changes in the evaluation of patients with sepsis and septic shock. Methods A retrospective analysis was made of 135 patients who were diagnosed as "sepsis"or "septic shock" according to sepsis 3. 0 diagnostic criteria in Shanxi Provincial People's Hospital from May 2020 to February 2022. According to the final diagnosis, 135 patients were divided into sepsis group (n=70) and septic shock group (n=65). Recording all relevant clinical and laboratory data of patients and comparing the differences of each index between the different groups. By using SPSS 26. 0 software, binary logistic regression was used to screen the risk factors affecting the severity of sepsis, and the receiver operating characteristic curve was used to analyze the evaluation value of PCT and ΔPCT in the severity and prognosis of sepsis. The difference in P＜0.05 is statistically significant. Results Comparing the relevant data of sepsis group and septic shock group, The PCT1［12.14(1.50, 58.32)ng/mL］, PCT2［9.47(1.09, 48.38)ng/mL］, Lac［2.49(1.65, 3.68)mmol/L］, in septic shock group were higher than those in sepsis group; The difference was statistically significant (P＜0.05). Multivariate logistic regression analysis showed that PCT2(OR:1.054, 95%CI:1.004~1.106, P=0.033) and Lac (OR:1.472, 95%CI:1.036~2.091, P=0.031) were the risk factors affecting the severity of sepsis. ROC curve analysis showed that there was little difference between PCT2［AUC: 0.784 (95%CI: 0.708~0.860), P＜0.001］ and Lac［AUC:0.768(95%CI:0.688~0.847), P＜0.001］ in the evaluation of sepsis severity, and the evaluation efficiency was higher after the combination of the two indexes［AUC: 0.821(95%CI:0.750~0.891), P＜0.001］. Conclusion The serum PCT value at 48 hours after admission (PCT2) can be used as an indicator for evaluating septic shock, PCT2 combined with Lac is more valuable in evaluating septic shock