Abstract: Objective To investigate the clinical effect of heated humidified high flow nasal cannula ventilation(HHFNC) in the treatment of severe pneumonia in infants. 
Methods A total of 80 children with severe pneumonia admitted to our hospital were selected as the research subjects and randomly divided into mask oxygen inhalation group(control group, n=40) and HHFNC group(experimental group, n=40) by random number table method. The changes in partial pressure oxygen(PaO2), partial pressure of carbon dioxide(PCO2), and PaO2/fraction of inspiration O2(FiO2) of the two groups were compared before treatment and at 2 h, 24 h, and 48 h after treatment. The relief time of dyspnea(nasal flaring and three-concave sign)，the length of hospitalization and the rate of endotracheal intubation were compared.
Results Before treatment, PaO2, PCO2, PaO2/ FiO2 of the two groups were compared, and the differences was not statistically significant(P＞0.05). After treatment，PaO2 and PaO2/FiO2 in two groups increased gradually，while PCO2 decreased gradually; PaO2 and PaO2/FiO2 in HHFNC group were higher than those in control group，while PCO2 was lower than those in control group; there were significant differences in the interaction among groups，time points and time points between groups(P＜0.05). The relief time of dyspnea and the length of hospitalization were shorter, the rate of endotracheal intubation was lower in HHFNC group than in the control group, and the differences were statistically significant（P＜0.05）. 
Conclusion HHFNC in the treatment of severe pneumonia in infants can improve the condition, shorten the length of hospitalization, and reduce the rate of tracheal intubation, and the effect is significant.

Key words: pneumonia , continuous positive airway pressure, infants