Objective To investigate the application value of lung ultrasonic on severe high altitude pulmonary edema.Methods A prospective, single-blind, case-control study was conducted. Sixty patients with severe high altitude pulmonary edema admitted to Qinghai University Affiliated Hospital from February 2015 to May 2017 were enrolled. The patients were divided into 2500-3000 m group, 3000-3500 m group and 3500-4200 m group according to different altitudes,with 20 patients in each group. The acute physiology and chronic health evaluationⅡ(APACHEⅡ) score was recorded before and 12 hours and 24 hours after treatment. The arterial partial pressure of oxygen (PaO2) was determined by blood gas analysis, and the oxygenation index (PaO2/FiO2) was calculated. Bedside ultrasound scanning was used to determine B line number and pulmonary artery pressure (PAP), and B line score was calculated to reflect lung water content. The correlation between B line score and PaO2/FiO2, PAP and APACHEⅡ scores at each time point was analyzed by Pearson correlation analysis.Results None of 60 patients died or exited, all of them were enrolled in the final analysis. There was no significant difference in PaO2/FiO2, PAP, APACHEⅡ score or B line score among different altitudes groups (allP > 0.05). Repeated measurement variance analysis showed that the effects of different altitudes on PaO2/FiO2, PAP, APACHEⅡ score and B line score were not statistically significant (F value was 0.312, 0.014, 1.098, 0.236, andP value was 0.340, 0.791, 0.733, and 0.986, respectively). The PaO2/FiO2, PAP, APACHEⅡ score and B line score in all groups were improved obviously from 12 hours after treatment, and the improvements at 24 hours were more than those at 12 hours (allP < 0.05). Repeated measurement variance analysis showed that the effect at different time points on PaO2/FiO2, PAP, APACHEⅡ score and B line score was statistically significant (F value was 1844.270, 121.690, 1173.175, 19426.968, allP < 0.001). The interaction effects of different altitudes and different time points on PaO2/FiO2, PAP, APACHEⅡ score and B line score were not statistically significant (F value was 0.304, 0.404, 1.172, 1.403, andP value was 0.875, 0.805, 0.327, and 0.591, respectively). Pearson correlation analysis showed that there was a significant negative correlation between B line score and PaO2/FiO2 before and after treatment (r value was -0.579, -0.522, and -0.386, allP < 0.01), indicating that the more the B line, the more severe the pulmonary edema, and the worse the oxygenation; with the decrease in B line after treatment, the pulmonary edema was gradually alleviated, and oxygenation was gradually improved. There was a significant positive correlation between B line score and APACHEⅡ score before and 24 hours after treatment (r value was 0.484 and 0.536, bothP < 0.01), indicating that the more the B line, the more severe the patient; with the decrease in B line after treatment, the patient's condition improved after treatment. There was only a weak correlation between B line score and PAP at 24 hours after treatment (r = 0.317,P = 0.014), indicating that PAP was not a sensitive indicator in the degree of pulmonary edema in patients.Conclusions The more the B line in patients with severe high altitude pulmonary edema,the more severe of the pulmonary edema, and the more severe of the patient. There was no significant correlation between the B line score and PAP. Pulmonary ultrasonography can still be used not only in the plain and low elevation areas, but in the high altitude areas, as a reliable method to evaluate the severity of pulmonary edema.