Objective To investigate the clinical effect of bedside ultrasound in patients with severe pneumonia and mechanical ventilation. Methods A total of 87 patients with pneumonia in ventilator ventilation in the Department of Critical Medicine from May 2016 to August 2018 in our hospital were taken as the research objects. Patients were examined by bedside ultrasound, CT, and laboratory. The diagnostic value of B-mode ultrasound in patients with severe pneumonia and mechanical ventilation. Results Bedside B-ultrasound showed the pulmonary consolidation of severe pneumonia (68.09%), the number of subpleural lesions (4.73 ± 2.57), and number of intercostal changes of pleura (8.12 ± 2.26) and pulmonary ultrasound scores (21.31 ± 5.26)of the severe pneumonia groups compared with the non-severe pneumonia groups (7.50%, 2.02 ± 1.08, 2.47 ± 1.02, 30.86 ± 5.72) were significantly different (P <0.05);The patients with pleural effusion in the severe pneumonia group (38.30%) compared with the non-severe pneumonia group (17.75%) has a higher proportion, but the difference was not statistically significant (P> 0.05). The sensitivity and specificity of bedside ultrasound and CT examination items were both higher, and there was no significant difference between the two (P> 0.05). In the severe pneumonia group, 9 died and 38 survived. Bedside ultrasonography showed lung consolidation (100%), number of subpleural lesions (5.31 ± 2.27), number of intercostal intercostal changes (9.25 ± 2.46), and pulmonary ultrasound score (21.31 ± 5.26) in patients with severe pneumonia. Compared with the surviving patients (60.53%, 3.79 ± 1.97, 6.54 ± 1.85, 25.27 ± 2.85 points), the difference was significant (P <0.05); The patients with pleural effusion (77.78%) and the surviving patients (55.26) %), But the difference is not statistically significant (P> 0.05). Conclusion Bedside ultrasound can accurately determine the lung characteristics of patients with severe pneumonia and mechanical ventilation, which is of great value for diagnosis and prognosis of patients.