Objective To investigate the failure factors of no-invasive ventilation (NIV) as an initial ventilation mode for the treatment of community acquired pneumonia (CAP). Methods Totally 237 cases of CAP patients with NIV as initial ventilation were analyzed retrospectively in the emergency department of Beijing Chaoyang Hospital. According to the failure of NIV, patients were divided into two groups. General clinical data and acute physiological and chronic health score (APACHEⅡ), physiological parameters, pulmonary infection and the prognosis of the patients were recorded, and were compared between the two groups. The risk factors of NIV1 hour and 3 hours later were analyzed by multivariate logistic regression. Results Compared with the NIV failure group, the mortality of the patients in the NIV successful group (17.6 and 35.6, P< 0.01) was significantly lower. The risk factors for the NIV1 hour failure of the patients included the APACHE Ⅱ score(OR=1.352,95%CI:1.132-3.015,P=0.035),the hemodynamic support (OR=9.826,95%CI:2.525-86.377,P=0.002) and the severity of the pulmonary infection, and the risk factors for the physiological index of the failure of NIV3 hours included hemodynamic support(OR=6.365,95%CI:2.552-28.316,P=0.004),respiratory frequency and pH value. Conclusions Hemodynamic support is the most important risk factor for the failure of NIV in CAP patients. During the NIV treatment, the patients' respiratory frequency, pH and blood pressure should be closely monitored to ensure the success and safety of the treatment. Key words: NIV; CAP; Hemodynamic support; Respiratory frequency; pHvalue