Background: A meta-analysis was conducted to investigate the effects of the 45° semi-recumbent position on the clinical outcomes of mechanically ventilated patients. Methods:The PubMed, Embase, and Cochrane medical databases were searched using the keywords "45°", "head-of-bed elevation", and "semi-recumbent". All relevant randomized controlled trials (RCTs) published between 2005 and 2021 were obtained. The Cochrane system for randomized intervention was adopted and the RevMan 5.3.5 software was used to construct forest plots and funnel plots to assess the risk of bias for the included studies.Results: A total of 128 literatures were initially screened for this meta-analysis, and 7 studies were finally included, with a total of 740 patients. Meta-analysis revealed that the incidence of ventilator-associated pneumonia (VAP) was significantly lower in patients in the 45° semi-recumbent position compared to patients in the 30° semi-recumbent position [odds ratio (OR) =0.48; 95% confidence interval (CI): 0.28 to 0.84; Z=2.59; P=0.009]. Furthermore, the incidence of gastric reflux was significantly lower in patients in the 45° semi-recumbent position compared to patients in the 30° semi-recumbent position (OR =0.50; 95% CI: 0.27 to 0.96; Z=2.09; P=0.04). Meta-analysis demonstrated that the incidence of pressure sores was significantly higher in patients in the 45° semi-recumbent position compared to patients in the 30° semirecumbent position (OR =1.88; 95% CI: 1.05 to 3.36; Z=2.11; P=0.03).Discussion: The 45° semi-recumbent position can reduce the incidence of VAP and gastric reflux in patients undergoing mechanical ventilation (MV), but it may also increase the risk of pressure sores. Thus, consideration should be made based on a comprehensive understanding of the patient's condition and physical state.