Severe bronchial asthma complicated with respiratory failure, a common critical illness in respiratory medicine, may be lifethreatening. High-flow nasal cannula (HFNC) is a novel oxygen therapy technique developed in recent years. HFNC was applied in this study for treating adult patients with severe bronchial asthma complicated with respiratory failure. Its efficacy was analyzed comparatively to conventional oxygen therapy (COT). HFNC and COT were randomly performed based on conventional treatment. e HFNC group was similar to COT-treated patients in terms of response rate, with no significant difference in efficacy between the two groups. In patients with bronchial asthma, effectively increased PO 2 and reduced PCO 2 were observed after treatment in both groups. However, HFNC was more efficient than COT in elevating PO 2 in patients with severe bronchial asthma complicated with respiratory failure, while no statistically significant difference in PCO 2 reduction was found between the two groups. Heart rate (HR) and respiratory rate (RR) between the two groups on admission (0 h) and at 2, 8, 24, and 48 h after admission were compared. Both indicators significantly decreased with time. No significant differences in HR and RR were found between the groups at 0, 2, and 8 h after admission. However, these indicators were significantly lower in the HFNC group compared with the COT group at 24 and 48 h after admission. HFNC could significantly elevate PO 2 and reduce HR and RR. us, it is a promising option for patients with severe bronchial asthma complicated with respiratory failure.