Background: The changes before and after fluid resuscitation in patients with septic shock and their relationship with prognosis have rarely been reported. Objectives: We aimed to observe the correlation between pulmonary vascular permeability index (PVPI), shock index (SI), and severity of septic shock. Methods: This case-control study retrospectively analyzed the clinical data of 154 patients with septic shock treated at our hospital (Weifang, China) from October 2016 to October 2018. They were divided into a survival group or a death group according to the 28day prognosis. Univariate analysis was performed for vital signs, the acute physiology and chronic health evaluation II (APACHE-II) score, the sequential organ failure assessment (SOFA) score at admission, SI at admission (SI1), SI at 3 h after fluid resuscitation (SI2), PVPI at admission (PVPI1), PVPI at 3 h after fluid resuscitation (PVPI2), and lactate clearance rate (LCR). The correlations of PVPI and SI with the APACHE-II score, SOFA score, and LCR were analyzed by plotting the receiver operating characteristic curves. Results: Among the 154 cases, 70 survived after 28 days and 84 died. We observed that SI1, SI2, PVPI1, PVPI2, APACHE-II score, and SOFA score were significantly lower in the survival group than in the death group, while LCR was significantly higher (P < 0.05). Also, SI1, SI2, PVPI1, and PVPI2 were positively correlated with APSCHE-II and SOFA scores of patients with septic shock, but negatively correlated with LCR (P < 0.05). Moreover, SI2 predicted the prognosis of patients with septic shock significantly better than SI1, PVPI1, and PVPI2 did. When SI2 was 1.22, the Youden index was 0.822, the sensitivity was 91.23%, the specificity was 89.47%, the positive predictive value was 0.912, and the negative predictive value was 0.924. The positive and negative likelihood ratios were 0.897 and 0.375, respectively. Conclusions: Based on the study, SI after fluid resuscitation was more valuable for evaluating the prognosis of patients with septic shock than SI at admission, as well as PVPI values at admission and after fluid resuscitation.