Objective To investigate the value of serum aquaporin 1 （AQP1） level combined with extravascular lung water index （EVLWI） in assessing the severity and prognosis of sepsis causing acute respiratory distress syndrome （ARDS）. Methods 268 patients with sepsis-induced ARDS （ARDS group） and 55 patients with sepsis alone （sepsis alone group） admitted to our hospital from January 2020 to December 2023 were selected. Patients with sepsis-induced ARDS were divided into 89 mild， 109 moderate， and 70 severe groups according to the oxygenation index （OI）， and 104 deaths and 164 survivors according to the 28 d prognosis. Detection of serum AQP1 levels and calculation of EVLWI. Using Spearman's method， the correlation between serum AQP1 level， EVLWI and OI in patients with sepsis-induced ARDS； the establishment of a logistic regression model to determine the factors of sepsis-induced mortality in patients with ARDS； and the plotting of ROC curves to evaluate the value of serum AQP1 level in combination with EVLWI for its assessment. Results Compared with the simple sepsis group， serum AQP1 level was reduced and EVLWI was increased in the ARDS group （P < 0.05）. AQP1 levels were sequentially lower and EVLWI sequentially higher in the mild， moderate， and severe groups （P < 0.05）. Serum AQP1 levels were positively correlated with OI in patients with sepsis-induced ARDS， and EVLWI was negatively correlated with OI in patients with sepsis-induced ARDS （P < 0.05）. The 28 d mortality rate in 268 patients with ARDS due to sepsis was 38.81% （104/268）. The independent protective factors for death in ARDS patients with sepsis were elevated OI （OR= 0.984， 95%CI： 0.976 ~ 0.992） and elevated AQP1 （OR= 0.761， 95%CI： 0.677 ~ 0.854）， and the independent risk factors were increased SOFA score （OR= 1.367， 95%CI： 1.142 ~ 1.636） and elevated blood lactate （OR= 2.515， 95%CI： 1.689 ~ 3.745）， and elevated EVLWI （OR= 1.559， 95%CI： 1.290 ~ 1.885） （P < 0.05）. The AUC predicted by serum AQP1 level combined with EVLWI was 0.887 （95%CI： 0.843 ~ 0.923）， which was greater than the AUC predicted by serum AQP1 level， and EVLWI alone， which was 0.792 （95%CI： 0.738 ~ 0.839）， and 0.807 （95%CI： 0.754 ~ 0.852） （P < 0.05）. Conclusion Decreased serum AQP1 levels and elevated EVLWI were associated with increased severity and poor prognosis in patients with sepsis-induced ARDS， and serum AQP1 levels in combination with EVLWI were of high value in assessing the prognosis of patients with sepsis-induced ARDS.