Objective To explore the optimal position for mechanical ventilation in patients with chronic obstructive pulmonary di-sease （COPD）, and to provide empirical evidence for clinical nursing practice.Methods A total of 120 COPD patients on mechanical ventilation were selected.Diaphragmatic function was measured using bedside ultrasound when the patient was positioned supine and in 30, 40, and 60 degrees Trendelenburg, respectively. Parameters of mechanical ventilation were also recorded.Results There were statistically significant differences in diaphragmatic movement among the four positions (all P＜0.05), with better perfor-mance observed in the 30 and 40 degrees Trendelenburg position. In different positions during mechanical ventilation, smaller Trendelenburg position tilt angle was associated with better airway compliance, higher inspiratory resistance, and lower expiratory resistance, as well as lower support pressure and better ventilation effectiveness (all P＜0.05).Conclusion There are noticeable trends in the function of the diaphragm and mechanical ventilation effectiveness as a result of the different body postures in COPD patients.In general, it is recommended to choose 30-40 degrees Trendelenburg position for mechanical ventilation.