Abstract： Objective To compare the efficacy of high flow nasal cannula oxygen therapy (HFNC) and non-invasive ventilation (NIV) in the treatment of chronic obstructive pulmonary disease (COPD) with acute-moderate type Ⅱ respiratory failure,and to explore the feasibility of HFNC in the treatment of COPD with respiratory failure.Methods Patients diagnosed with COPD with acute moderate type Ⅱ respiratory failure (Arterial blood gas pH 7.25-7.35,PaCO2＞ 50 mmHg) admitted to the ICUs from April 2017 to December 2017 were retrospectively analyzed.All patients who were treated with HFNC within the first 4 hours after the admission to the ICUs,and continued for more than 2 hours and for at least 4 hours within the first 24 hours were included in the HFNC group.Those treated with NIV in the same conditions were included in the NIV group.The end point was the failure rates of treatment (changing to respiratory support method in another group or invasive ventilation) and 28-day mortality.Results Eighty-two patients (39 in the HFNC group and 43 in the NIV group) were enrolled.The HFNC group had a treatment failure rate of 28.2％,which was lower than that of the NIV group (39.5％).However,Kaplan-Meier curve analysis showed no significant difference between the two groups (Log Rank test 1.228,P=0.268).The 28-day mortality rate in HFNC group was 15.4％,which was no different from 14％ in NIV group (Log Rank test 0.049,P=0.824).The number of airway care interventions within the first 24 hours was significantly lower in the HFNC group than in the NIV group [5 (3～8) vs.11 (7～15)],whereas the duration of respiratory support within the first 24 hours was significantly longer in the HFNC group than in the NIV group [16 (9～22) hours vs.8 (4～11) hours] (all P＜0.05).The incidence of nasal facial lesions in the NIV group was 20.9％,significantly higher than that of HFNC group (5.1％,P ＜0.05).Conclusion For COPD with acute moderate type Ⅱ respiratory failure,HFNC has similar therapeutic effects as NIV.HFNC has better therapeutic tolerance and is a new potential respiratory support method for clinical treatment of COPD with respiratory failure.