Objective:To evaluate the prognostic value of plasma microRNA-30b-5p (miR-30b-5p) combined with extravascular lung water index (EVLWI) in patients with acute respiratory distress syndrome (ARDS).Methods:120 ARDS patients admitted to Danzhou People's Hospital from January 2016 to June 2019 were enrolled. The gender, age, body mass index (BMI), underlying diseases, etiology and baseline values of heart rate (HR), respiratory rate (RR), oxygenation index (OI), arterial partial pressure of carbon dioxide (PaCO 2) and acute physiology and chronic health evaluation Ⅱ (APACHE Ⅱ) score were collected. According to the survival outcome during hospitalization, the patients were divided into survival group and death group. According to OI, the patients were divided into mild-moderate group (OI > 100 mmHg, 1 mmHg = 0.133 kPa) and severe group (OI ≤ 100 mmHg). The expression of plasma miR-30b-5p was detected by real-time fluorescence quantitative reverse transcription-polymerase chain reaction (RT-PCR), and EVLWI was measured. The receiver operating characteristic (ROC) curve was drawn to analyze the value of plasma miR-30b-5p and EVLWI in predicting the death of patients with ARDS. Pearson correlation method was used to analyze the correlation between miR-30b-5p and EVLWI in ARDS patients with different prognosis during hospitalization. Results:120 patients with ARDS were enrolled in the analysis, with 42 patients in the death group, and 78 in the survival group; with 67 patients in the mild-moderate group, and 53 in the severe group. APACHE Ⅱ score in the death group was higher than that in the survival group, but there was no significant difference in gender, age, BMI, underlying diseases, etiology or baseline values of HR, RR, OI, or PaCO 2 between the two groups. The expression of plasma miR-30b-5p and EVLWI level in the death group were significantly higher than those in the survival group [miR-30b-5p (2 -ΔΔCt): 2.28±0.74 vs. 0.52±0.06, EVLWI (mL/kg): 15.38±4.60 vs. 10.24±2.15, both P < 0.01]. The expression of plasma miR-30b-5p, EVLWI and mortality during hospitalization in the severe group were significantly higher than those in the mild-moderate group [miR-30b-5p (2 -ΔΔCt): 2.05±0.65 vs. 0.93±0.17, EVLWI (mL/kg): 14.65±4.20 vs. 11.36±2.28, mortality during hospitalization: 58.5% (31/53) vs. 16.4% (11/67), all P < 0.01]. ROC curve analysis showed that the best cut-off value of plasma miR-30b-5p and EVLWI in predicting the death during hospitalization of ARDS patients were 1.62 and 13.28 mL/kg, respectively. Moreover, the area under ROC curve (AUC) of the combination of two parameters was significantly higher than that of the two alone (0.897 vs. 0.827, 0.785), with high sensitivity and specificity, 90.5% and 84.2%, respectively. Pearson correlation analysis showed that plasma miR-30b-5p in dead ARDS patients was significantly positively correlated with EVLWI ( r = 0.768, P < 0.01), but the correlation was not found in surviving patients ( r = 0.118, P > 0.05). Conclusion:The expression of plasma miR-30b-5p and EVLWI are related to the severity and prognosis of patients with ARDS, and the combination of the two has certain evaluation value for the prognosis of ARDS patients.