Objective：To evaluate the value of the difference between peripheral venous and arterial lactate level for the prognosis of patients with septic shock after early resuscitation. Methods：Patients with septic shock in the Department of Critical Care Medicine，Affiliated Hospital of Integration of Chinese and Western Medicine，Nanjing University of Chinese Medicine from May 2017 to May 2018 were enrolled in this prospective observational study. Patients were divided into two groups according to the 28-day mortality. Peripheral venous and arterial blood samples were withdrawn simultaneously and analyzed immediately at the bedside on admission and after 6 h-bundles of treatments. Peripheral venous lactate concentration（V-Lac）and arterial lactate concentration（A-Lac）were recorded，while the difference between V-Lac and A-Lac（ΔLac） was calculated. Multivariate logistic regression analysis was performed to select possible risk factors for 28-day mortality，and the receiver operating characteristic curve（ROC） was plotted to assess the prognostic value for 28-day mortality. Results：Fifty-nine patients were enrolled. Thirty-four patients survived and twenty-five patients died during the 28-day period. Compared with the survivor group，acute physiology and chronic health evaluation Ⅱ score（APACHE Ⅱ）and acute physiology and chronic health evaluation Ⅱ score（SOFA）were significantly higher in the non-survivor group（P < 0.05）. In the non-survivor group，A-Lac and V-Lac were significantly higher at admission（P < 0.05），and V-Lac and ΔLac were significantly higher after 6 h-bundles of treatments（P < 0.05）. Multivariate logistic regression analysis showed that ΔLac after 6 h-bundles of treatments（OR=74.107，P=0.005）was the independent risk factors for 28-day mortality. It was shown by ROC curve analysis that the maximum area under the ROC curve（AUC）of ΔLac was 0.838（P < 0.001）.When the best cut-off value was 0.65 mmol/L as a predictor of 28-day mortality，the sensitivity was 76.0% and the specificity was 85.3%. Conclusion：The presence of ΔLac after the early resuscitation of septic shock is associated with worse outcomes. It can be used to gauge the severity of tissue hypofusion and to estimate poor outcome of patients with septic shock.