OBJECTIVE: To evaluate the effect of high-flow nasal cannula oxygen (HFNO) therapy on hospital length of stay (LOS) and postoperative pulmonary complications (PPCs) in adult postoperative patients. DATA SOURCES: PubMed, Embase, the Cochrane Library, Web of Science of Studies, China National Knowledge Index, and Wan Fang databases were searched until July 2018. STUDY SELECTION: Randomized controlled trials (RCTs) comparing HFNO with conventional oxygen therapy or noninvasive mechanical ventilation in adult postoperative patients were included. The primary outcomes were hospital LOS and PPCs; short-term mortality (defined as intensive care unit, hospital, or 28-day mortality) and intubation rate were the secondary outcomes. DATA EXTRACTION: Demographic variables, high-flow oxygen therapy application, effects, and side effects were retrieved. Data were analyzed by the methods recommended by the Cochrane Collaboration. The strength of evidence was assessed by the Grading of Recommendations Assessment, Development and Evaluation. Random errors were evaluated with trial sequential analysis. DATA SYNTHESIS: Fourteen studies (2568 patients) met the inclusion criteria and were included. Compared to the control group, the pooled effect showed that HFNO was significantly associated with a shorter hospital stay (mean difference: -0.81; 95% confidence interval [CI]: -1.34 to -0.29, = .002), but not mortality (risk ratio [RR]: 1.0, 95% CI: 0.63 to 1.59, = 1.0). Weak evidence of a reduction in reintubation rate (RR: 0.76, 95% CI: 0.57-1.01, = .06) and PPC rate (RR: 0.89, 95% CI: 0.75-1.06, = .18) with HFNO versus control group was recorded. CONCLUSIONS: The available RCTs suggest that, among the adult postoperative patients, HFNO therapy compared to the control group significantly reduces hospital LOS.