Objective:To investigate the clinical application of optimized preoxygenation with nasal high flow humidification oxygen therapy before tracheal intubation in critically ill patients.Methods:The100 critically ill patients who needed emergency tracheal intubation in ZhejiangYiwu Central Hospital from June 2018 to June 2019 were selected as the research objects. According to the random number table method, they were randomly divided into observation group (50 cases) and control group (50 cases). The vital signs were continuously monitored in both groups. After the supine position was taken, the airway was opened by traditional methods to remove oral and respiratory secretions. The patients in the control group were given pressure oxygen by balloon mask, while the patients in the observation group were given pre-oxygenation by nasal high flow humidification oxygen therapy. The time required to achieve the goal of pre-oxygenation, blood gas analysis, SpO 2 changes and abdominal distension before and after pre-oxygenation and after intubation were compared between the two groups. Results:In observation group, time required to reach the target preoxygenation was faster than control group: (4.34 ± 0.56) min vs. (7.62 ± 1.43) min ( P<0.05). In the observation group, PaO 2 preoxygenation and immediately after intubation were higher than those in control group: (67.25 ± 2.34) mmHg (1 mmHg=0.133 kPa) vs. (61.87 ± 2.65) mmHg, (62.46 ± 3.51) mmHg vs. (56.32 ± 3.98) mmHg; while those after PaCO 2 preoxygenation and immediately after intubationwere lower than those in control group: (38.78 ± 2.68) mmHg vs. (43.12 ± 2.95) mmHg, (42.57 ± 2.65) mmHg vs. (49.46 ± 3.43) mmHg, the differences were statistically significant ( P<0.05). In observation group, SpO 2 preoxygenation and immediately after intubation were higher than those control group: 0.97 ± 0.03 vs. 0.92 ± 0.03, 0.92 ± 0.03 vs. 0.88 ± 0.05, the differences were statistically significant ( P<0.05). In observation group, the incidence of abdominal distension was lower than that in control group: 4.00%(2/50) vs. 24.00% (12/50), the difference was statistically significant ( P<0.05). Conclusions:Optimized preoxygenation with nasal high flow humidification oxygen therapy has a good effect before tracheal intubation in critically ill patients. It can improve the blood oxygen level and reduce complications.