Objective To investigate the effect of bronchoalveolar lavage guided by fiberoptic bronchoscopy on the blood gas indicators and pentraxin-3 (PTX3) level in severe pneumonia patients complicated with respiratory failure. Methods A retrospective analysis was performed on 60 severe pneumonia patients complicated with respiratory failure admitted to our hospital from February 2016 to January 2018. According to undergoing fiberoptic bronchoscopy-guided bronchoalveolar lavage or not, 29 patients were assigned into the study group and 31 patients into the control group. The patients of both groups were given symptomatic treatment, such as assistant ventilation, anti-infective therapy, phlegm resolving treatment and maintenance of internal environment stability. While, the patients of the study group were given bronchoalveolar lavage guided by nasal or tracheal bronchoscopy. Oxygen index (OI), arterial partial pressure of carbon dioxide (PaCO₂) and arterial oxygen saturation (SaO₂) before and 24h after bronchoalveolar lavage, levels of C-reactive protein (CRP) and PTX3 before and 1,3 and 7 d (D1, D3 and D7) after bronchoalveolar lavage, and length and mortality in intensive care unit (ICU) within 30 d were compared between the 2 groups. SPSS statistics 17.0 was used for data analysis.Results After 24h lavage, the study group and control group had their OI [(280.2±22.3) vs (180.5±12.9)mmHg(1mmHg＝0.133kPa), (228.4±18.5) vs (183.4±13.8)mmHg], PaCO₂ [(39.3±5.5) vs (47.7±7.3)mmHg, (43.5±6.2) vs (47.2±7.9)mmHg] and SaO₂ [(94.2±2.9)% vs (85.8±5.0)%, (90.4±4.3)% vs (85.8±5.0)%] improved when compared with the values before bronchoalveolar lavage. The study group had significantly higher OI and SaO₂, but lower PaCO₂ than the control group 24h after lavage (P<0.05). Compared with before bronchoalveolar lavage, CRP level was increased at D1 and then decreased significantly at D3 and D7, and PTX3 level was decreased at D1, D3 and D7 (all P<0.05). The levels of CRP [(108.4±21.5) vs (117.5±30.4)mg/L, (66.9±13.5) vs (74.5±16.3)mg/L, (25.1±9.2) vs (34.6±7.3)mg/L] and PTX3 [(18.3±4.0) vs (20.8±3.6)ng/ml, (12.5±3.1) vs (15.9±3.5)ng/ml, (5.2±2.3) vs (9.0±2.9)ng/ml] were obviously lower in the study group at D1, D 3 and D7 than in the control group (P<0.05). The length of ICU stay was remarkably shorter in the study group than in the control group [(8.3±3.7) vs (13.5±5.4)d, P<0.05]. Conclusion Bronchoalveolar lavage can improve respiratory function, reduce PTX3 level and shorten ICU stay length in severe pneumonia patients complicated with respiratory failure.