Objective To investigate the impact of high-flow nasal cannula (HFNC) combined with fiberoptic bronchoscopy alveolar lavage (BAL) on clinical symptom and prognosis of severe pneumonia. Methods A total of 84 patients with severe pneumonia admitted to No. 989 Hospital of Joint Logistic Support Force of the Chinese People’s Liberation Army from May 2022 to October 2025 were selected and divided into observation group (n＝42) and control group (n＝42) by random number table method. The control group received routine symptomatic treatment combined with HFNC, while the observation group was additionally treated with fiberoptic BAL on the basis of the control group. Blood gas analysis indexes (partial pressure of arterial oxygen (PaO2), partial pressure of arterial carbon dioxide (PaCO2), arterial oxygen saturation (SaO2), oxygenation index (OI)), inflammatory factors (C-reactive protein (CRP), procalcitonin (PCT), interleukin-6 (IL-6), tumor necrosis factor- α (TNF- α)), symptom improvement time (body temperature recovery, cough relief, disappearance of pulmonary rales), respiratory function indexes, clinical efficacy and prognostic indicators (length of intensive care unit (ICU) stay, total length of hospital stay, tracheal intubation rate, 28-day mortality) were compared between the two groups before and after treatment. Results PaO2, SaO2 and OI after treatment of patients in the observation group were significantly higher than those in the control group during the same period (all P＜0.05), and PaCO2, levels of serum CRP, PCT, IL-6, TNF-α were significantly lower than those in the control group (all P＜0.05). The time for body temperature to return to normal, cough relief, lung rale disappearance, ICU stay, total hospital stay, tracheal intubation rate, and 28-day mortality rate in the observation group were all significantly lower than those in the control group (all P＜0.05). Conclusion HFNC combined with fiberoptic BAL can rapidly improve oxygenation status and clinical symptoms of patients with severe pneumonia, effectively inhibit inflammatory response, shorten hospital stay, reduce tracheal intubation rate and mortality, and significantly improve short-term prognosis.